pointer/keyboard: Remove focus_resource_listener

In order to support multiple pointers for the same client, we're
going to need to kill it.

This will cause crashes for now, but will be fixed by the next
commit.

src/wayland/meta-wayland-pointer.h

@@ -49,7 +49,6 @@ struct _MetaWaylandPointer
   MetaWaylandSurface *focus_surface;
   struct wl_listener focus_surface_listener;
   struct wl_resource *focus_resource;
-  struct wl_listener focus_resource_listener;
   guint32 focus_serial;
   guint32 click_serial;