block: kill unused polling bits in __blkdev_direct_IO()

With addition of __blkdev_direct_IO_async(), __blkdev_direct_IO() now
serves only multio-bio I/O, which we don't poll. Now we can remove
anything related to I/O polling from it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b8c597a6b7ee612df394853bfd24726aee5b898e.1635337135.git.asml.silence@gmail.com


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