Change bumpfee result value from 'oldfee' to 'origfee'.

The result value indicates the actual fee on the transaction that was replaced. But there is an error message which uses the description 'oldfee' to refer to the original fee rate applied to the new transaction's estimated max size.  It was confusing that two different uses of 'oldfee' had two different numeric values.

src/wallet/rpcwallet.cpp

@@ -2674,7 +2674,7 @@ UniValue bumpfee(const JSONRPCRequest& request)
             "\nResult:\n"
             "{\n"
             "  \"txid\":    \"value\",   (string)  The id of the new transaction\n"
-            "  \"oldfee\":  n,         (numeric) Fee of the replaced transaction\n"
+            "  \"origfee\":  n,         (numeric) Fee of the replaced transaction\n"
             "  \"fee\":      n,         (numeric) Fee of the new transaction\n"
             "}\n"
             "\nExamples:\n"
@@ -2899,7 +2899,7 @@ UniValue bumpfee(const JSONRPCRequest& request)
 
     UniValue result(UniValue::VOBJ);
     result.push_back(Pair("txid", wtxBumped.GetHash().GetHex()));
-    result.push_back(Pair("oldfee", ValueFromAmount(nOldFee)));
+    result.push_back(Pair("origfee", ValueFromAmount(nOldFee)));
     result.push_back(Pair("fee", ValueFromAmount(nNewFee)));
 
     return result;