Get rid of PendingWalletTx class.

No reason for this class to exist if it doesn't have any code to run in the
destructor. e10e1e8db0 from
https://github.com/bitcoin/bitcoin/pull/16208 recently removed code destructor
code that would return an unused key if the transaction wasn't committed.

src/interfaces/wallet.h

@@ -34,7 +34,6 @@ struct CRecipient;
 namespace interfaces {
 
 class Handler;
-class PendingWalletTx;
 struct WalletAddress;
 struct WalletBalances;
 struct WalletTx;
@@ -134,13 +133,19 @@ public:
     virtual void listLockedCoins(std::vector<COutPoint>& outputs) = 0;
 
     //! Create transaction.
-    virtual std::unique_ptr<PendingWalletTx> createTransaction(const std::vector<CRecipient>& recipients,
+    virtual CTransactionRef createTransaction(const std::vector<CRecipient>& recipients,
         const CCoinControl& coin_control,
         bool sign,
         int& change_pos,
         CAmount& fee,
         std::string& fail_reason) = 0;
 
+    //! Commit transaction.
+    virtual bool commitTransaction(CTransactionRef tx,
+        WalletValueMap value_map,
+        WalletOrderForm order_form,
+        std::string& reject_reason) = 0;
+
     //! Return whether transaction can be abandoned.
     virtual bool transactionCanBeAbandoned(const uint256& txid) = 0;
 
@@ -288,21 +293,6 @@ public:
     virtual std::unique_ptr<Handler> handleCanGetAddressesChanged(CanGetAddressesChangedFn fn) = 0;
 };
 
-//! Tracking object returned by CreateTransaction and passed to CommitTransaction.
-class PendingWalletTx
-{
-public:
-    virtual ~PendingWalletTx() {}
-
-    //! Get transaction data.
-    virtual const CTransaction& get() = 0;
-
-    //! Send pending transaction and commit to wallet.
-    virtual bool commit(WalletValueMap value_map,
-        WalletOrderForm order_form,
-        std::string& reject_reason) = 0;
-};
-
 //! Information about one wallet address.
 struct WalletAddress
 {