drm/omap: remove unused function defines

Remove driver (un)register API defines. They do not even exist
anymore.
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/dss/omapdss.h

@@ -585,9 +585,6 @@ struct omap_dss_driver {
 
 bool omapdss_is_initialized(void);
 
-int omap_dss_register_driver(struct omap_dss_driver *);
-void omap_dss_unregister_driver(struct omap_dss_driver *);
-
 int omapdss_register_display(struct omap_dss_device *dssdev);
 void omapdss_unregister_display(struct omap_dss_device *dssdev);