io_uring: kill stale comment for io_cqring_overflow_kill()

This function now deals only with discarding overflow entries on ring
free and exit, and it no longer returns whether we successfully flushed
all entries as there's no CQE posting involved anymore. Kill the
outdated comment.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -666,7 +666,6 @@ static void io_cq_unlock_post(struct io_ring_ctx *ctx)
 	io_commit_cqring_flush(ctx);
 }
 
-/* Returns true if there are no backlogged entries after the flush */
 static void io_cqring_overflow_kill(struct io_ring_ctx *ctx)
 {
 	struct io_overflow_cqe *ocqe;