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/tasks/ManualPositionSmoothVel/FlightTaskManualPositionSmoothVel.hpp

@@ -50,7 +50,6 @@ class FlightTaskManualPositionSmoothVel : public FlightTaskManualPosition
 {
 public:
 	FlightTaskManualPositionSmoothVel() = default;
-
 	virtual ~FlightTaskManualPositionSmoothVel() = default;
 
 	bool activate(const trajectory_setpoint_s &last_setpoint) override;