API: x11: Change GDK_WINDOW_XDISPLAY() macro

Instead of lots of magic, we can go the usual way of requesting the
XDisplay of the window's display. So we do that.

gdk/x11/gdkx.h

@@ -176,7 +176,7 @@ gint     gdk_x11_get_default_screen       (void);
 
 #define GDK_DISPLAY_XDISPLAY(display) (gdk_x11_display_get_xdisplay (display))
 
-#define GDK_WINDOW_XDISPLAY(win)      (gdk_x11_drawable_get_xdisplay (gdk_x11_window_get_drawable_impl (win)))
+#define GDK_WINDOW_XDISPLAY(win)      (GDK_DISPLAY_XDISPLAY (gdk_window_get_display (win)))
 
 /**
  * GDK_WINDOW_XID: