io_uring: kill unnecessary io_run_ctx_fallback() in io_ring_exit_work()

We already run the fallback task_work in io_uring_try_cancel_requests(),
no need to duplicate at ring exit explicitly.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8519,7 +8519,6 @@ static void io_ring_exit_work(struct work_struct *work)
 	 */
 	do {
 		io_uring_try_cancel_requests(ctx, NULL, NULL);
-		io_run_ctx_fallback(ctx);
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 	io_ring_ctx_free(ctx);
 }