message: core: removed some leftover debugging defines
diff: #include <future>
  #include <utility>
  -// Set to 1 to log incoming/outgoing mavlink messages.
  -#define MESSAGE_DEBUGGING 0
  -
  namespace mavsdk {
  SystemImpl::SystemImpl(MavsdkImpl& parent) :
  @@ -475,9 +472,6 @@ bool SystemImpl::send_message(mavlink_message_t& message)
  }
  }
  -#if MESSAGE_DEBUGGING == 1
  - LogDebug() << "Sending msg " << size_t(message.msgid);
  -#endif
  return _parent.send_message(message);
  }
  