FlightTask: Weather vane cleanup

Remove the entire external yaw handler, dynamic memory allocation,
pointer passing logic. Directly instanciate the weather vane instance
in the flight tasks that support it.

src/modules/flight_mode_manager/FlightModeManager.hpp

@@ -131,7 +131,6 @@ private:
 		FlightTaskIndex index{FlightTaskIndex::None};
 	} _current_task{};
 
-	WeatherVane *_wv_controller{nullptr};
 	int8_t _old_landing_gear_position{landing_gear_s::GEAR_KEEP};
 	uint8_t _takeoff_state{takeoff_status_s::TAKEOFF_STATE_UNINITIALIZED};
 	int _task_failure_count{0};