io_uring/poll: remove outdated comments of caching

io_uring/poll: remove outdated comments of caching

Previous commit 13a99017ff19 ("io_uring: remove events caching
atavisms") entirely removes the events caching optimization introduced
by commit 81459350d581 ("io_uring: cache req->apoll->events in
req->cflags"). Hence the related comment should also be removed to avoid
misunderstanding.

Fixes: 13a99017ff19 ("io_uring: remove events caching atavisms")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Link: https://lore.kernel.org/r/20221110060313.16303-1-linma@zju.edu.cn
Signed-off-by: Jens Axboe <axboe@kernel.dk>