The member btrfs_fs_info::scrub_nocow_workers is unused since the nocow
optimization was removed from scrub in 
9bebe665c3e4 ("btrfs: scrub:
Remove unused copy_nocow_pages and its callchain").
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
        refcount_t scrub_workers_refcnt;
        struct btrfs_workqueue *scrub_workers;
        struct btrfs_workqueue *scrub_wr_completion_workers;
-       struct btrfs_workqueue *scrub_nocow_workers;
        struct btrfs_workqueue *scrub_parity_workers;
 
 #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY