wayland: Mark ourselves as not supporting bounding shapes

Theoretically, we apply the shape mask client-side ourselves
with an ARGB32 pixmap and intersect it to get a union shape,
but I don't particularly care enough to write that code.

Realistic application code using bounding shapes in 2014 is
quite rare.

gdk/wayland/gdkdisplay-wayland.c

@@ -404,7 +404,7 @@ gdk_wayland_display_store_clipboard (GdkDisplay    *display,
 static gboolean
 gdk_wayland_display_supports_shapes (GdkDisplay *display)
 {
-  return TRUE;
+  return FALSE;
 }
 
 static gboolean