ACM: no need to fetch offsets at startup

AP_Param handles this

ArduCopter/sensors.pde

@@ -94,7 +94,6 @@ static void init_compass()
         return;
     }
     dcm.set_compass(&compass);
-    compass.get_offsets();					// load offsets to account for airframe magnetic interference
     compass.null_offsets_enable();
 }