Btrfs: cleanup fs_info->hashers

fs_info->hashers is now an obsolete one.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>

fs/btrfs/ctree.h

@@ -1253,7 +1253,6 @@ struct btrfs_fs_info {
 	struct mutex reloc_mutex;
 
 	struct list_head trans_list;
-	struct list_head hashers;
 	struct list_head dead_roots;
 	struct list_head caching_block_groups;
 

fs/btrfs/disk-io.c

@@ -1984,7 +1984,6 @@ int open_ctree(struct super_block *sb,
 	INIT_LIST_HEAD(&fs_info->trans_list);
 	INIT_LIST_HEAD(&fs_info->dead_roots);
 	INIT_LIST_HEAD(&fs_info->delayed_iputs);
-	INIT_LIST_HEAD(&fs_info->hashers);
 	INIT_LIST_HEAD(&fs_info->delalloc_inodes);
 	INIT_LIST_HEAD(&fs_info->ordered_operations);
 	INIT_LIST_HEAD(&fs_info->caching_block_groups);