vmem: do not explicitly delete the window

The window variable is set to "none" anyway, so there will be no
windows to delete.

modules/video_output/vmem.c

@@ -216,8 +216,6 @@ static int Open(vlc_object_t *object)
     vd->display = Display;
     vd->control = Control;
 
-    /* */
-    vout_display_DeleteWindow(vd, NULL);
     return VLC_SUCCESS;
 }