Tracker: remove definition of Devo constructor

AntennaTracker/GCS_Tracker.cpp

@@ -111,5 +111,4 @@ void GCS_Tracker::update_sensor_status_flags()
 }
 
 // avoid building/linking Devo:
-AP_DEVO_Telem::AP_DEVO_Telem() {}
 void AP_DEVO_Telem::init() {};