Remove opt-in RBF

Remove the option to signal or not signal for BIP 125 (Opt-in Full Replace-By-Fee).
By removing the option in the GUI it will fallback to the wallet configuration which by default is
true unless the user changed it using CLI.

src/qt/forms/sendcoinsdialog.ui

@@ -1049,16 +1049,6 @@ Note:  Since the fee is calculated on a per-byte basis, a fee rate of "100 satos
              </item>
             </layout>
            </item>
-           <item>
-            <widget class="QCheckBox" name="optInRBF">
-             <property name="text">
-              <string>Enable Replace-By-Fee</string>
-             </property>
-             <property name="toolTip">
-              <string>With Replace-By-Fee (BIP-125) you can increase a transaction's fee after it is sent. Without this, a higher fee may be recommended to compensate for increased transaction delay risk.</string>
-             </property>
-            </widget>
-           </item>
           </layout>
          </widget>
         </item>

src/qt/sendcoinsdialog.cpp

@@ -179,13 +179,6 @@ void SendCoinsDialog::setModel(WalletModel *_model)
         connect(ui->groupFee, &QButtonGroup::idClicked, this, &SendCoinsDialog::coinControlUpdateLabels);
 
         connect(ui->customFee, &BitcoinAmountField::valueChanged, this, &SendCoinsDialog::coinControlUpdateLabels);
-#if (QT_VERSION >= QT_VERSION_CHECK(6, 7, 0))
-        connect(ui->optInRBF, &QCheckBox::checkStateChanged, this, &SendCoinsDialog::updateSmartFeeLabel);
-        connect(ui->optInRBF, &QCheckBox::checkStateChanged, this, &SendCoinsDialog::coinControlUpdateLabels);
-#else
-        connect(ui->optInRBF, &QCheckBox::stateChanged, this, &SendCoinsDialog::updateSmartFeeLabel);
-        connect(ui->optInRBF, &QCheckBox::stateChanged, this, &SendCoinsDialog::coinControlUpdateLabels);
-#endif
         CAmount requiredFee = model->wallet().getRequiredFee(1000);
         ui->customFee->SetMinValue(requiredFee);
         if (ui->customFee->value() < requiredFee) {
@@ -195,9 +188,6 @@ void SendCoinsDialog::setModel(WalletModel *_model)
         updateFeeSectionControls();
         updateSmartFeeLabel();
 
-        // set default rbf checkbox state
-        ui->optInRBF->setCheckState(Qt::Checked);
-
         if (model->wallet().hasExternalSigner()) {
             //: "device" usually means a hardware wallet.
             ui->sendButton->setText(tr("Sign on device"));
@@ -360,17 +350,12 @@ bool SendCoinsDialog::PrepareSendText(QString& question_string, QString& informa
         question_string.append("<span style='color:#aa0000; font-weight:bold;'>");
         question_string.append(BitcoinUnits::formatHtmlWithUnit(model->getOptionsModel()->getDisplayUnit(), txFee));
         question_string.append("</span><br />");
-
-        // append RBF message according to transaction's signalling
-        question_string.append("<span style='font-size:10pt; font-weight:normal;'>");
-        if (ui->optInRBF->isChecked()) {
-            question_string.append(tr("You can increase the fee later (signals Replace-By-Fee, BIP-125)."));
-        } else {
-            question_string.append(tr("Not signalling Replace-By-Fee, BIP-125."));
-        }
-        question_string.append("</span>");
     }
 
+    // append RBF message
+    question_string.append("<span style='font-size:10pt; font-weight:normal;'>");
+    question_string.append(tr("You can increase the fee later."));
+
     // add total amount in all subdivision units
     question_string.append("<hr />");
     CAmount totalAmount = m_current_transaction->getTotalTransactionAmount() + txFee;
@@ -834,7 +819,6 @@ void SendCoinsDialog::updateCoinControlState()
     // Avoid using global defaults when sending money from the GUI
     // Either custom fee will be used or if not selected, the confirmation target from dropdown box
     m_coin_control->m_confirm_target = getConfTargetForIndex(ui->confTargetSelector->currentIndex());
-    m_coin_control->m_signal_bip125_rbf = ui->optInRBF->isChecked();
 }
 
 void SendCoinsDialog::updateNumberOfBlocks(int count, const QDateTime& blockDate, double nVerificationProgress, SyncType synctype, SynchronizationState sync_state) {

src/qt/test/wallettests.cpp

@@ -75,17 +75,13 @@ void ConfirmSend(QString* text = nullptr, QMessageBox::StandardButton confirm_ty
 }
 
 //! Send coins to address and return txid.
-Txid SendCoins(CWallet& wallet, SendCoinsDialog& sendCoinsDialog, const CTxDestination& address, CAmount amount, bool rbf,
+Txid SendCoins(CWallet& wallet, SendCoinsDialog& sendCoinsDialog, const CTxDestination& address, CAmount amount,
                   QMessageBox::StandardButton confirm_type = QMessageBox::Yes)
 {
     QVBoxLayout* entries = sendCoinsDialog.findChild<QVBoxLayout*>("entries");
     SendCoinsEntry* entry = qobject_cast<SendCoinsEntry*>(entries->itemAt(0)->widget());
     entry->findChild<QValidatedLineEdit*>("payTo")->setText(QString::fromStdString(EncodeDestination(address)));
     entry->findChild<BitcoinAmountField*>("payAmount")->setValue(amount);
-    sendCoinsDialog.findChild<QFrame*>("frameFee")
-        ->findChild<QFrame*>("frameFeeSelection")
-        ->findChild<QCheckBox*>("optInRBF")
-        ->setCheckState(rbf ? Qt::Checked : Qt::Unchecked);
     Txid txid;
     btcsignals::scoped_connection c(wallet.NotifyTransactionChanged.connect([&txid](const Txid& hash, ChangeType status) {
         if (status == CT_NEW) txid = hash;
@@ -283,8 +279,8 @@ void TestGUI(interfaces::Node& node, const std::shared_ptr<CWallet>& wallet)
     // Send two transactions, and verify they are added to transaction list.
     TransactionTableModel* transactionTableModel = walletModel.getTransactionTableModel();
     QCOMPARE(transactionTableModel->rowCount({}), 105);
-    Txid txid1 = SendCoins(*wallet.get(), sendCoinsDialog, PKHash(), 5 * COIN, /*rbf=*/false);
-    Txid txid2 = SendCoins(*wallet.get(), sendCoinsDialog, PKHash(), 10 * COIN, /*rbf=*/true);
+    Txid txid1 = SendCoins(*wallet.get(), sendCoinsDialog, PKHash(), 5 * COIN);
+    Txid txid2 = SendCoins(*wallet.get(), sendCoinsDialog, PKHash(), 10 * COIN);
     // Transaction table model updates on a QueuedConnection, so process events to ensure it's updated.
     qApp->processEvents();
     QCOMPARE(transactionTableModel->rowCount({}), 107);
@@ -424,7 +420,7 @@ void TestGUIWatchOnly(interfaces::Node& node, TestChain100Setup& test)
     timer.start(500);
 
     // Send tx and verify PSBT copied to the clipboard.
-    SendCoins(*wallet.get(), sendCoinsDialog, PKHash(), 5 * COIN, /*rbf=*/false, QMessageBox::Save);
+    SendCoins(*wallet.get(), sendCoinsDialog, PKHash(), 5 * COIN, QMessageBox::Save);
     const std::string& psbt_string = QApplication::clipboard()->text().toStdString();
     QVERIFY(!psbt_string.empty());
 

src/qt/walletmodel.cpp

@@ -464,7 +464,6 @@ WalletModel::UnlockContext::~UnlockContext()
 bool WalletModel::bumpFee(Txid hash, Txid& new_hash)
 {
     CCoinControl coin_control;
-    coin_control.m_signal_bip125_rbf = true;
     std::vector<bilingual_str> errors;
     CAmount old_fee;
     CAmount new_fee;