fs, iomap: remove IOCB_DIO_CALLER_COMP

fs, iomap: remove IOCB_DIO_CALLER_COMP

This was added by commit 099ada2c8726 ("io_uring/rw: add write support
for IOCB_DIO_CALLER_COMP") and disabled a little later by commit
838b35bb6a89 ("io_uring/rw: disable IOCB_DIO_CALLER_COMP") because it
didn't work.  Remove all the related code that sat unused for 2 years.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20251113170633.1453259-2-hch@lst.de
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>