io_uring: inline io_poll_remove_waitqs

Inline io_poll_remove_waitqs() into its only user and clean it up.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2f1a91a19ffcd591531dc4c61e2f11c64a2d6a6d.1628536684.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>