Merge #15408: Remove unused TransactionError constants

fa9b60c842 Remove unused TransactionError constants (MarcoFalke)

Pull request description:

  Fixup to #14978, which introduced a bunch of unused enum values, such as `UNKNOWN_ERROR`, `ERROR_COUNT` and `TRANSACTION_ERR_LAST`. None of those have a meaning in the context of an `enum class`, where the compiler can infer if all cases have been covered in a switch-case.

  Also, move the global `::maxTxFee` back to the rpc caller, so it can be set on a per call basis (in the future).

Tree-SHA512: 7f1e2d795f1c1278ecd54ddab2b92c2a862f3c637b482d1d008208925befa1c9dd4b3c4bb1bfcbc5ca4b66a41004aaf01ea96ea95236f944250b8a6cf99ff173

src/rpc/rawtransaction.cpp

@@ -1065,10 +1065,11 @@ static UniValue sendrawtransaction(const JSONRPCRequest& request)
 
     bool allowhighfees = false;
     if (!request.params[1].isNull()) allowhighfees = request.params[1].get_bool();
+    const CAmount highfee{allowhighfees ? 0 : ::maxTxFee};
     uint256 txid;
-    TransactionError err;
     std::string err_string;
-    if (!BroadcastTransaction(tx, txid, err, err_string, allowhighfees)) {
+    const TransactionError err = BroadcastTransaction(tx, txid, err_string, highfee);
+    if (TransactionError::OK != err) {
         throw JSONRPCTransactionError(err, err_string);
     }
 
@@ -1493,8 +1494,8 @@ UniValue combinepsbt(const JSONRPCRequest& request)
     }
 
     PartiallySignedTransaction merged_psbt;
-    TransactionError error;
-    if (!CombinePSBTs(merged_psbt, error, psbtxs)) {
+    const TransactionError error = CombinePSBTs(merged_psbt, psbtxs);
+    if (error != TransactionError::OK) {
         throw JSONRPCTransactionError(error);
     }