[wallet] Remove return value from CommitTransaction()

CommitTransaction returns a bool to indicate success, but since commit
b3a74100b8 it only returns true, even if the transaction was not
successfully broadcast. This commit changes CommitTransaction() to return
void.

All dead code in `if (!CommitTransaction())` branches has been removed.

src/qt/sendcoinsdialog.cpp

@@ -558,8 +558,7 @@ void SendCoinsDialog::processSendCoinsReturn(const WalletModel::SendCoinsReturn
     msgParams.second = CClientUIInterface::MSG_WARNING;
 
     // This comment is specific to SendCoinsDialog usage of WalletModel::SendCoinsReturn.
-    // WalletModel::TransactionCommitFailed is used only in WalletModel::sendCoins()
-    // all others are used only in WalletModel::prepareTransaction()
+    // All status values are used only in WalletModel::prepareTransaction()
     switch(sendCoinsReturn.status)
     {
     case WalletModel::InvalidAddress:
@@ -581,10 +580,6 @@ void SendCoinsDialog::processSendCoinsReturn(const WalletModel::SendCoinsReturn
         msgParams.first = tr("Transaction creation failed!");
         msgParams.second = CClientUIInterface::MSG_ERROR;
         break;
-    case WalletModel::TransactionCommitFailed:
-        msgParams.first = tr("The transaction was rejected with the following reason: %1").arg(sendCoinsReturn.reasonCommitFailed);
-        msgParams.second = CClientUIInterface::MSG_ERROR;
-        break;
     case WalletModel::AbsurdFee:
         msgParams.first = tr("A fee higher than %1 is considered an absurdly high fee.").arg(BitcoinUnits::formatWithUnit(model->getOptionsModel()->getDisplayUnit(), model->wallet().getDefaultMaxTxFee()));
         break;

src/qt/walletmodel.cpp

@@ -260,9 +260,7 @@ WalletModel::SendCoinsReturn WalletModel::sendCoins(WalletModelTransaction &tran
         }
 
         auto& newTx = transaction.getWtx();
-        std::string rejectReason;
-        if (!wallet().commitTransaction(newTx, {} /* mapValue */, std::move(vOrderForm), rejectReason))
-            return SendCoinsReturn(TransactionCommitFailed, QString::fromStdString(rejectReason));
+        wallet().commitTransaction(newTx, {} /* mapValue */, std::move(vOrderForm));
 
         CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
         ssTx << *newTx;

src/qt/walletmodel.h

@@ -139,7 +139,6 @@ public:
         AmountWithFeeExceedsBalance,
         DuplicateAddress,
         TransactionCreationFailed, // Error returned when wallet is still locked
-        TransactionCommitFailed,
         AbsurdFee,
         PaymentRequestExpired
     };