Drop UpdateTransaction in favor of UpdateInput

Updating the input explicitly requires the caller to present a mutable
input, which more clearly communicates the effects and intent of the method.

In most cases, this input is already immediately available and need not be
looked up.

src/wallet/wallet.cpp

@@ -2608,7 +2608,7 @@ bool CWallet::SignTransaction(CMutableTransaction &tx)
     // sign the new tx
     CTransaction txNewConst(tx);
     int nIn = 0;
-    for (const auto& input : tx.vin) {
+    for (auto& input : tx.vin) {
         std::map<uint256, CWalletTx>::const_iterator mi = mapWallet.find(input.prevout.hash);
         if(mi == mapWallet.end() || input.prevout.n >= mi->second.tx->vout.size()) {
             return false;
@@ -2619,7 +2619,7 @@ bool CWallet::SignTransaction(CMutableTransaction &tx)
         if (!ProduceSignature(*this, TransactionSignatureCreator(&txNewConst, nIn, amount, SIGHASH_ALL), scriptPubKey, sigdata)) {
             return false;
         }
-        UpdateTransaction(tx, nIn, sigdata);
+        UpdateInput(input, sigdata);
         nIn++;
     }
     return true;
@@ -3050,7 +3050,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CTransac
                     strFailReason = _("Signing transaction failed");
                     return false;
                 } else {
-                    UpdateTransaction(txNew, nIn, sigdata);
+                    UpdateInput(txNew.vin.at(nIn), sigdata);
                 }
 
                 nIn++;