This field is never used, so remove it. Last use was probably in
23ea8e5a ("Btrfs: load checksum data once when submitting a direct
read io").
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>