gimbal: don't spoof gimbal device (#24271)

The current approach was wrong because the gimbal protocol now
handles the case properly where the autopilot is in charge of a
non-MAVLink gimbal.

This means that we don't need to send message "as if we were a gimbal
device" and instead set thet gimbal_device_id to 1 (up to 6) to indicate
we are in charge or a non-MAVLink gimbal.

src/modules/gimbal/output_mavlink.cpp

@@ -109,6 +109,9 @@ void OutputMavlinkV1::update(const ControlData &control_data, bool new_setpoints
 
 	_stream_device_attitude_status();
 
+	// If the output is MAVLink v1, then we signal this by referring to compid 1.
+	gimbal_device_id = 1;
+
 	_last_update = now;
 }