Btrfs: fix unused members in struct btrfs_root

There isn't any real use of following members of struct btrfs_root
so delete them.

struct kobject root_kobj;
struct completion kobj_unregister;
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ctree.h

@@ -1798,8 +1798,6 @@ struct btrfs_root {
 	struct btrfs_fs_info *fs_info;
 	struct extent_io_tree dirty_log_pages;
 
-	struct kobject root_kobj;
-	struct completion kobj_unregister;
 	struct mutex objectid_mutex;
 
 	spinlock_t accounting_lock;

fs/btrfs/disk-io.c

@@ -1275,12 +1275,10 @@ static void __setup_root(u32 nodesize, u32 sectorsize, u32 stripesize,
 	memset(&root->root_key, 0, sizeof(root->root_key));
 	memset(&root->root_item, 0, sizeof(root->root_item));
 	memset(&root->defrag_progress, 0, sizeof(root->defrag_progress));
-	memset(&root->root_kobj, 0, sizeof(root->root_kobj));
 	if (fs_info)
 		root->defrag_trans_start = fs_info->generation;
 	else
 		root->defrag_trans_start = 0;
-	init_completion(&root->kobj_unregister);
 	root->root_key.objectid = objectid;
 	root->anon_dev = 0;