codec/avcodec/vaapi_x11.c: Do not free x11 visual.

The macro DefaultVisual only returns an reference and not an allocation.

modules/codec/avcodec/vaapi_x11.c

@@ -178,7 +178,6 @@ static void DestroyWindow(vout_display_t *vd)
 {
     vout_display_sys_t *sys = (vout_display_sys_t *) vd->sys;
 
-    XFree(sys->x11.visual); /* ?? */
     if (sys->x11.window)
     {
         XUnmapWindow(sys->conn->p_display_x11, sys->x11.window);