message: core: don't filter from UDP_BRIDGE anymore
  I think we can remove this because we no longer check for any heartbeat
  to see if something is connected but we should actually check for
  `has_autopilot()` or `has_camera` to determine what we have available.
diff: @@ -195,12 +195,6 @@ void SystemImpl::remove_call_every(const void* cookie)
  void SystemImpl::process_heartbeat(const mavlink_message_t& message)
  {
  - // FIXME: for now we ignore heartbeats from UDP_BRIDGE because that's just
  - // confusing since it doesn't mean a vehicle is connected.
  - if (message.compid == MAV_COMP_ID_UDP_BRIDGE) {
  - return;
  - }
  -
  mavlink_heartbeat_t heartbeat;
  mavlink_msg_heartbeat_decode(&message, &heartbeat);
  