io_uring: kill outdated comment about overflow flush

__io_cqring_overflow_flush() doesn't return anything anymore, remove
outdate comment.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4ce2bcbb17eac80cdf883fd1459d5ee6586e238c.1674484266.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -666,7 +666,6 @@ static void io_cqring_overflow_kill(struct io_ring_ctx *ctx)
 	}
 }
 
-/* Returns true if there are no backlogged entries after the flush */
 static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx)
 {
 	size_t cqe_size = sizeof(struct io_uring_cqe);