drm/omap: dss: Remove omapdss_atv_ops get_wss and set_wss operations

The operations are never used, remove them. If the need to set wide
screen signaling data arises later, it should be implemented by
extending the DRM bridge API.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>