message: [RPC] Remove warning about wallet addresses in createmultisig()
  createmultisig() was updated in V0.16 to not use the wallet. Warning
  text was included to warn the user. Remove that now.
diff: @@ -114,8 +114,7 @@ static UniValue createmultisig(const JSONRPCRequest& request)
  if (IsHex(keys[i].get_str()) && (keys[i].get_str().length() == 66 || keys[i].get_str().length() == 130)) {
  pubkeys.push_back(HexToPubKey(keys[i].get_str()));
  } else {
  - throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Invalid public key: %s\nNote that from v0.16, createmultisig no longer accepts addresses."
  - " Users must use addmultisigaddress to create multisig addresses with addresses known to the wallet.", keys[i].get_str()));
  + throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Invalid public key: %s\n.", keys[i].get_str()));
  }
  }
  