drbd: Remove superfluous declaration

Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -689,7 +689,6 @@ struct drbd_work {
 	drbd_work_cb cb;
 };
 
-struct drbd_tl_epoch;
 struct drbd_request {
 	struct drbd_work w;
 	struct drbd_conf *mdev;