mc_pos_control: remove useless landed state copy

If the landed state was set before the position controller starts it
would get updated with the first poll_subscriptions() anyways. But it's
not on all posix and nuttx platforms I tested and the deleted statement
just copies the zero message into the struct which is already zero.

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -588,9 +588,6 @@ MulticopterPositionControl::run()
 	// get an initial update for all sensor and status data
 	poll_subscriptions();
 
-	// We really need to know from the beginning if we're landed or in-air.
-	orb_copy(ORB_ID(vehicle_land_detected), _vehicle_land_detected_sub, &_vehicle_land_detected);
-
 	hrt_abstime t_prev = 0;
 
 	// Let's be safe and have the landing gear down by default