AP_HAL: track simulated ADSB vehicles relative to simulation origin

removes dependence on ArduPilot AHRS library

Also removes vehicles based off vehicle simulated position rather than distance-from-origin, so you always have company

libraries/AP_HAL/SIMState.cpp

@@ -99,6 +99,7 @@ void SIMState::fdm_input_local(void)
     // ride_along.receive(input);
 
     // update the model
+    sitl_model->update_home();
     sitl_model->update_model(input);
 
     // get FDM output from the model