Remove LNDMC_ALT_MAX

This should be replaced with the maximum geofence
altitude GF_MAX_VER_DIST. I'm not aware anyone is using
this functionality as is.

src/modules/navigator/rtl_direct.cpp

@@ -349,8 +349,6 @@ void RtlDirect::set_rtl_item()
 
 	} else {
 		// Convert mission item to current position setpoint and make it valid.
-		mission_apply_limitation(_mission_item);
-
 		if (mission_item_to_position_setpoint(_mission_item, &pos_sp_triplet->current)) {
 			_navigator->set_position_setpoint_triplet_updated();
 		}