mc_pos_control: remove unused var

src/modules/mc_pos_control/MulticopterPositionControl.hpp

@@ -108,8 +108,6 @@ private:
 
 	hrt_abstime	_time_stamp_last_loop{0};		/**< time stamp of last loop iteration */
 
-	int _task_failure_count{0};         /**< counter for task failures */
-
 	vehicle_local_position_setpoint_s _setpoint {};
 	vehicle_control_mode_s _vehicle_control_mode {};