io_uring: remove unused hash_wait

No users of io_uring_ctx::hash_wait left, kill it.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e25cb83c233a5f75f15275596b49fbafbea606fa.1617287883.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -455,8 +455,6 @@ struct io_ring_ctx {
 	/* exit task_work */
 	struct callback_head		*exit_task_work;
 
-	struct wait_queue_head		hash_wait;
-
 	/* Keep this last, we don't need it for the fast path */
 	struct work_struct		exit_work;
 	struct list_head		tctx_list;