io_uring: get rid of files in exit cancel

We don't match against files on cancellation anymore, so no need to drag
around files_struct anymore, just pass a flag telling whether only
inflight or all requests should be killed.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7bfc5409a78f8e2d6b27dec3293ec2d248677348.1621201931.git.asml.silence@gmail.com


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