io_uring: kill poll linking optimisation

With IORING_FEAT_FAST_POLL in place, io_put_req_find_next() for poll
requests doesn't make much sense, and in any case re-adding it
shouldn't be a problem considering batching in tctx_task_work(). We can
remove it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/15699682bf81610ec901d4e79d6da64baa9f70be.1639605189.git.asml.silence@gmail.com


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