[wallet] Move maxTxFee to wallet

This commit moves the maxtxfee setting to the wallet. There is only
one minor behavior change:

- an error message in feebumper now refers to -maxtxfee instead of
maxTxFee.

src/qt/sendcoinsdialog.cpp

@@ -578,7 +578,7 @@ void SendCoinsDialog::processSendCoinsReturn(const WalletModel::SendCoinsReturn
         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->node().getMaxTxFee()));
+        msgParams.first = tr("A fee higher than %1 is considered an absurdly high fee.").arg(BitcoinUnits::formatWithUnit(model->getOptionsModel()->getDisplayUnit(), model->wallet().getDefaultMaxTxFee()));
         break;
     case WalletModel::PaymentRequestExpired:
         msgParams.first = tr("Payment request expired.");

src/qt/walletmodel.cpp

@@ -222,9 +222,9 @@ WalletModel::SendCoinsReturn WalletModel::prepareTransaction(WalletModelTransact
         }
 
         // reject absurdly high fee. (This can never happen because the
-        // wallet caps the fee at maxTxFee. This merely serves as a
+        // wallet caps the fee at m_default_max_tx_fee. This merely serves as a
         // belt-and-suspenders check)
-        if (nFeeRequired > m_node.getMaxTxFee())
+        if (nFeeRequired > m_wallet->getDefaultMaxTxFee())
             return AbsurdFee;
     }