[logging] Don't log REJECT code when transaction is rejected

Remove the BIP61 REJECT code from error messages and logs when a
transaction is rejected.

BIP61 support was removed from Bitcoin Core in
fa25f43ac5. The REJECT codes will be
removed from the codebase entirely in the following commit.

src/util/validation.cpp

@@ -11,10 +11,9 @@
 /** Convert CValidationState to a human-readable message for logging */
 std::string FormatStateMessage(const CValidationState &state)
 {
-    return strprintf("%s%s (code %i)",
+    return strprintf("%s%s",
         state.GetRejectReason(),
-        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage(),
-        state.GetRejectCode());
+        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage());
 }
 
 const std::string strMessageMagic = "Bitcoin Signed Message:\n";