io_uring: remove __io_file_supports_nowait

Now that this only checks O_NONBLOCK and FMODE_NOWAIT, the helper is
complete overkilļ, and the comments are confusing bordering to wrong.
Just inline the check into the caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230620113235.920399-2-hch@lst.de


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