AP_AHRS: Remove unused uptime

libraries/AP_AHRS/AP_AHRS.h

@@ -542,9 +542,6 @@ public:
         return false;
     }
 
-    // time that the AHRS has been up
-    virtual uint32_t uptime_ms(void) const = 0;
-
     // get the selected ekf type, for allocation decisions
     int8_t get_ekf_type(void) const {
         return _ekf_type;

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -1075,14 +1075,3 @@ bool AP_AHRS_DCM::healthy(void) const
     // consider ourselves healthy if there have been no failures for 5 seconds
     return (_last_failure_ms == 0 || AP_HAL::millis() - _last_failure_ms > 5000);
 }
-
-/*
-  return amount of time that AHRS has been up
- */
-uint32_t AP_AHRS_DCM::uptime_ms(void) const
-{
-    if (_last_startup_ms == 0) {
-        return 0;
-    }
-    return AP_HAL::millis() - _last_startup_ms;
-}

libraries/AP_AHRS/AP_AHRS_DCM.h

@@ -102,9 +102,6 @@ public:
     // is the AHRS subsystem healthy?
     bool healthy() const override;
 
-    // time that the AHRS has been up
-    uint32_t uptime_ms() const override;
-
 private:
     float _ki;
     float _ki_yaw;