ivi-shell: remove struct link_screen

link_screen's sole purpose is to link a layer to multiple screens, if
the layer should be shown in multiple screens.  This can be only
achieved, if surfaces of the layer have multiple weston_views dedicated
to the different screens.

Current implementation assumes in many places that a ivi_surface has
only one weston_view.  Therefore, a layer can be only shown on one
screen.

Although this (a layer on multiple screens) is a nice to have feature
for ivi-shell, it is not very crucial.  In any case, it is not an easy
task to implement this feature, because it has lot of corner cases.

I removed with this patch the link_screen data structure, because it
does not have any purpose in current implementation.

Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
Tested-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
Reviewed-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
[Pekka: Line-wrapped commit message.]
diff --git a/ivi-shell/ivi-layout-private.h b/ivi-shell/ivi-layout-private.h
index 074d598..a9dbdde 100644
--- a/ivi-shell/ivi-layout-private.h
+++ b/ivi-shell/ivi-layout-private.h
@@ -65,11 +65,11 @@
 struct ivi_layout_layer {
 	struct wl_list link;
 	struct wl_signal property_changed;
-	struct wl_list screen_list;
 	struct wl_list link_to_surface;
 	uint32_t id_layer;
 
 	struct ivi_layout *layout;
+	struct ivi_layout_screen *on_screen;
 
 	struct ivi_layout_layer_properties prop;
 	uint32_t event_mask;