AP_DAL: stop using airspeed_sensor_enabled from AP_DAL

this is an input to the EKF, but also populated based on the AHRS current state.

Make the data come from the sensor, not the *output* of the AHRS backends!

libraries/AP_DAL/AP_DAL.cpp

@@ -76,7 +76,6 @@ void AP_DAL::start_frame(AP_DAL::FrameType frametype)
     _RFRN.fly_forward = ahrs.get_fly_forward();
     _RFRN.takeoff_expected = ahrs.get_takeoff_expected();
     _RFRN.touchdown_expected = ahrs.get_touchdown_expected();
-    _RFRN.ahrs_airspeed_sensor_enabled = ahrs.airspeed_sensor_enabled(ahrs.get_active_airspeed_index());
     _RFRN.available_memory = hal.util->available_memory();
     _RFRN.ahrs_trim = ahrs.get_trim();
 #if AP_OPTICALFLOW_ENABLED

libraries/AP_DAL/AP_DAL.h

@@ -105,7 +105,7 @@ public:
         ARMED = (1U<<0),
         UNUSED = (1U<<1),
         FLY_FORWARD = (1U<<2),
-        AHRS_AIRSPEED_SENSOR_ENABLED = (1U<<3),
+        AHRS_AIRSPEED_SENSOR_ENABLED_UNUSED = (1U<<3),
         OPTICALFLOW_ENABLED = (1U<<4),
         WHEELENCODER_ENABLED = (1U<<5),
         TAKEOFF_EXPECTED = (1U<<6),
@@ -175,11 +175,6 @@ public:
 
     AP_DAL_Compass &compass() { return _compass; }
 
-    // random methods that AP_NavEKF3 wants to call on AHRS:
-    bool airspeed_sensor_enabled(void) const {
-        return _RFRN.ahrs_airspeed_sensor_enabled;
-    }
-
     // get apparent to true airspeed ratio; this is a sensor input
     // to the EKFs, captured from the barometer's atmosphere model
     // in start_frame():

libraries/AP_DAL/LogStructure.h

@@ -104,7 +104,7 @@ struct log_RFRN {
     uint8_t armed:1;
     uint8_t unused:1;  // was get_compass_is_null
     uint8_t fly_forward:1;
-    uint8_t ahrs_airspeed_sensor_enabled:1;
+    uint8_t ahrs_airspeed_sensor_enabled_unused:1;
     uint8_t opticalflow_enabled:1;
     uint8_t wheelencoder_enabled:1;
     uint8_t takeoff_expected:1;