Revert "io_uring: rename IORING_OP_FILES_UPDATE"

This reverts commit 4379d5f1.

We removed notification flushing, also cleanup uapi preparation changes
to not pollute it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/89edc3905350f91e1b6e26d9dbf42ee44fd451a2.1662027856.git.asml.silence@gmail.com


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