AP_DAL: stop using AHRS as conduit for Compass pointer

libraries/AP_DAL/AP_DAL.cpp

@@ -58,7 +58,6 @@ void AP_DAL::start_frame(AP_DAL::FrameType frametype)
     _RFRN.lat = _home.lat;
     _RFRN.lng = _home.lng;
     _RFRN.alt = _home.alt;
-    _RFRN.get_compass_is_null = AP::ahrs().get_compass() == nullptr;
     _RFRN.EAS2TAS = AP::baro().get_EAS2TAS();
     _RFRN.vehicle_class = ahrs.get_vehicle_class();
     _RFRN.fly_forward = ahrs.get_fly_forward();
@@ -257,15 +256,6 @@ void *AP_DAL::malloc_type(size_t size, Memory_Type mem_type) const
     return hal.util->malloc_type(size, AP_HAL::Util::Memory_Type(mem_type));
 }
 
-
-const AP_DAL_Compass *AP_DAL::get_compass() const
-{
-    if (_RFRN.get_compass_is_null) {
-        return nullptr;
-    }
-    return &_compass;
-}
-
 // map core number for replay
 uint8_t AP_DAL::logging_core(uint8_t c) const
 {

libraries/AP_DAL/AP_DAL.h

@@ -141,18 +141,8 @@ public:
     }
 #endif
 
-    // this method *always* returns you the compass.  This is in
-    // constrast to get_compass, which only returns the compass once
-    // the vehicle deigns to permit its use by the EKF.
     AP_DAL_Compass &compass() { return _compass; }
 
-    // this call replaces AP::ahrs()->get_compass(), whose return
-    // result can be varied by the vehicle (typically by setting when
-    // first reading is received).  This is explicitly not
-    // "AP_DAL_Compass &compass() { return _compass; } - but it should
-    // change to be that.
-    const AP_DAL_Compass *get_compass() const;
-
     // random methods that AP_NavEKF3 wants to call on AHRS:
     bool airspeed_sensor_enabled(void) const {
         return _RFRN.ahrs_airspeed_sensor_enabled;

libraries/AP_DAL/LogStructure.h

@@ -62,7 +62,7 @@ struct log_RFRN {
     uint8_t vehicle_class;
     uint8_t ekf_type;
     uint8_t armed:1;
-    uint8_t get_compass_is_null:1;
+    uint8_t unused:1;  // was get_compass_is_null
     uint8_t fly_forward:1;
     uint8_t ahrs_airspeed_sensor_enabled:1;
     uint8_t opticalflow_enabled:1;