mc stabilized mode: move from mc_pos_control to mc_att_control

- better in terms of dependencies:
  - the position controller code depended on position topics for yaw
  - mc_pos_control does not have to be run for Stabilized mode
- the code path is much simpler, and thus less error prone. This is
  especially important since Stabilized is often used as a fail-safe flight
  mode.

src/lib/FlightTasks/tasks/ManualPosition/FlightTaskManualPosition.cpp

@@ -53,10 +53,11 @@ bool FlightTaskManualPosition::updateInitialize()
 
 bool FlightTaskManualPosition::activate()
 {
-
 	// all requirements from altitude-mode still have to hold
 	bool ret = FlightTaskManualAltitude::activate();
 
+	_constraints.tilt = math::radians(MPC_TILTMAX_AIR.get());
+
 	// set task specific constraint
 	if (_constraints.speed_xy >= MPC_VEL_MANUAL.get()) {
 		_constraints.speed_xy = MPC_VEL_MANUAL.get();