libobs: Avoid request graphics lock after full_lock(scene).

As logic in video render thread, gs lock (obs_enter_graphics) should be requested before full_lock(scene).
However in function obs_sceneitem_group_ungroup called from UI thread, the order for requesting locks are contrary.

libobs/obs-scene.c

@@ -1867,9 +1867,7 @@ static obs_sceneitem_t *obs_scene_add_internal(obs_scene_t *scene,
 	}
 
 	if (item_texture_enabled(item)) {
-		obs_enter_graphics();
 		item->item_render = gs_texrender_create(GS_RGBA, GS_ZS_NONE);
-		obs_leave_graphics();
 	}
 
 	full_lock(scene);