AP_NavEKF: clean up unused variable lastDivergeTime_ms

libraries/AP_NavEKF/AP_NavEKF.cpp

@@ -3349,7 +3349,6 @@ void NavEKF::ZeroVariables()
     // initialise time stamps
     imuSampleTime_ms = hal.scheduler->millis();
     lastHealthyMagTime_ms = imuSampleTime_ms;
-    lastDivergeTime_ms = imuSampleTime_ms;
     TASmsecPrev = imuSampleTime_ms;
     BETAmsecPrev = imuSampleTime_ms;
     lastMagUpdate = imuSampleTime_ms;

libraries/AP_NavEKF/AP_NavEKF.h

@@ -342,7 +342,6 @@ private:
     AP_Int16 _hgtRetryTimeMode0;    // height measurement retry time following innovation consistency fail if GPS fusion mode is = 0 (msec)
     AP_Int16 _hgtRetryTimeMode12;   // height measurement retry time following innovation consistency fail if GPS fusion mode is > 0 (msec)
     uint32_t _magFailTimeLimit_ms;  // number of msec before a magnetometer failing innovation consistency checks is declared failed (msec)
-    uint32_t lastDivergeTime_ms;    // time in msec divergence of filter last detected
     float _gyroBiasNoiseScaler;     // scale factor applied to gyro bias state process variance when on ground
     float _magVarRateScale;         // scale factor applied to magnetometer variance due to angular rate
     uint16_t _msecGpsAvg;           // average number of msec between GPS measurements