AP_NavEKF2: remove unused terrainHgtStableSet_ms

libraries/AP_NavEKF2/AP_NavEKF2_VehicleStatus.cpp

@@ -473,7 +473,6 @@ void NavEKF2_core::setTouchdownExpected(bool val)
 // enabled by the combination of EK2_RNG_AID_HGT and EK2_RNG_USE_SPD parameters.
 void NavEKF2_core::setTerrainHgtStable(bool val)
 {
-    terrainHgtStableSet_ms = imuSampleTime_ms;
     terrainHgtStable = val;
 }
 

libraries/AP_NavEKF2/AP_NavEKF2_core.cpp

@@ -174,7 +174,6 @@ void NavEKF2_core::InitialiseVariables()
     lastVelReset_ms = 0;
     lastPosResetD_ms = 0;
     lastRngMeasTime_ms = 0;
-    terrainHgtStableSet_ms = 0;
 
     // initialise other variables
     gpsNoiseScaler = 1.0f;

libraries/AP_NavEKF2/AP_NavEKF2_core.h

@@ -1105,7 +1105,6 @@ private:
     uint32_t lastRngMeasTime_ms;            // Timestamp of last range measurement
     uint8_t rngMeasIndex[2];                // Current range measurement ringbuffer index for dual range sensors
     bool terrainHgtStable;                  // true when the terrain height is stable enough to be used as a height reference
-    uint32_t terrainHgtStableSet_ms;        // system time at which terrainHgtStable was set
 
     // Range Beacon Sensor Fusion
     obs_ring_buffer_t<rng_bcn_elements> storedRangeBeacon; // Beacon range buffer