message: [Trivial][RPC] Remove references to old command list-conf
  `startmasternode` `createmasternodebroadcast` error outputs are still
  referencing old command `list-conf` (deprecated since version v2.3.1).
  Replace with `listmasternodeconf`.
diff: @@ -435,7 +435,7 @@ UniValue startmasternode (const UniValue& params, bool fHelp)
  if(!found) {
  statusObj.push_back(Pair("success", false));
  - statusObj.push_back(Pair("error_message", "Could not find alias in config. Verify with list-conf."));
  + statusObj.push_back(Pair("error_message", "Could not find alias in config. Verify with listmasternodeconf."));
  }
  return statusObj;
  @@ -830,7 +830,7 @@ UniValue createmasternodebroadcast(const UniValue& params, bool fHelp)
  if(!found) {
  statusObj.push_back(Pair("success", false));
  - statusObj.push_back(Pair("error_message", "Could not find alias in config. Verify with list-conf."));
  + statusObj.push_back(Pair("error_message", "Could not find alias in config. Verify with listmasternodeconf."));
  }
  return statusObj;
  