Rover: move responsibility for logging into library

APMrover2/sensors.cpp

@@ -23,10 +23,6 @@ void Rover::update_compass(void)
 {
     if (AP::compass().enabled() && compass.read()) {
         ahrs.set_compass(&compass);
-        // update offsets
-        if (should_log(MASK_LOG_COMPASS)) {
-            logger.Write_Compass();
-        }
     }
 }
 

APMrover2/system.cpp

@@ -90,6 +90,7 @@ void Rover::init_ardupilot()
 #endif
 
     // initialise compass
+    AP::compass().set_log_bit(MASK_LOG_COMPASS);
     AP::compass().init();
 
     // initialise rangefinder