drm/omap: Remove declaration of nonexisting function

drm/omap: Remove declaration of nonexisting function

The omap_connector_attached_encoder() doesn't exist anymore, remove its
declaration from omap_connector.h.

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