Btrfs: drop useless LIST_HEAD in merge_reloc_root

Drop LIST_HEAD where the variable it declares is never used.

The uses were removed in 3fd0a558 ("Btrfs: Metadata ENOSPC
handling for balance"), but not the declaration.

The semantic patch that fixes this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
identifier x;
@@
- LIST_HEAD(x);
  ... when != x
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -2128,7 +2128,6 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
 					       struct btrfs_root *root)
 {
 	struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
-	LIST_HEAD(inode_list);
 	struct btrfs_key key;
 	struct btrfs_key next_key;
 	struct btrfs_trans_handle *trans = NULL;