btrfs: remove temporary btrfs_map_token declaration in ctree.h

This was added while I was moving this code to its new home, it can be
removed now.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -52,8 +52,6 @@ struct btrfs_balance_control;
 struct btrfs_delayed_root;
 struct reloc_control;
 
-struct btrfs_map_token;
-
 #define BTRFS_OLDEST_GENERATION	0ULL
 
 #define BTRFS_EMPTY_DIR_SIZE 0