fs: remove the now unused FMODE_* flags

FMODE_NDELAY, FMODE_EXCL and FMODE_WRITE_IOCTL were only used for
block internal purposed and are now entirely unused, so remove them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230608110258.189493-31-hch@lst.de


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