widget: Stop using child surface apis

All our surfaces are toplevels now, and thus all native.

gtk/gtkwidget.c

@@ -13201,10 +13201,6 @@ gtk_widget_render (GtkWidget            *widget,
   if (!GTK_IS_ROOT (widget))
     return;
 
-  /* We only render double buffered on native windows */
-  if (!gdk_surface_has_native (surface))
-    return;
-
   renderer = gtk_root_get_renderer (GTK_ROOT (widget));
   if (renderer == NULL)
     return;