FlightModeManager: correct setpoint struct initialization

It is important that setpoints get initialized with NAN and not overwritten
if specifically set by a successful flight task execution. It's then
clear if any setpoints were intentionally and successfully set.
Crucial for the position controller's emergency failsafe and the
seamless setpoint handover to the next flight task.

src/modules/flight_mode_manager/tasks/FlightTask/FlightTask.hpp

@@ -150,11 +150,6 @@ public:
 	 */
 	static const vehicle_local_position_setpoint_s empty_setpoint;
 
-	/**.
-	 * All counters are set to 0.
-	 */
-	static const ekf_reset_counters_s zero_reset_counters;
-
 	/**
 	 * Empty constraints.
 	 * All constraints are set to NAN.