Code review comment for lp:~vanvugt/mir/fix-1628794

This seems unnecessary complex. Do we still have to put mirprotobuf types on heap?

If not a stack variable would do the job.

If this is still the case I think you can get away with a make_unique<mp::Void>() and an empty callback .. like google::protobuf::NewCallback(google::protobuf::DoNothig) (bleh I wish this would be less verbose) so ignore_response can be removed too.