Btrfs: remove unused code when creating and merging reloc trees

In commit 5bc7247ac47c (Btrfs: fix broken nocow after balance) we started
abusing the rtransid and otransid fields of root items from relocation
trees to fix some issues with nodatacow mode. However later in commit
ba8b0289333a (Btrfs: do not reset last_snapshot after relocation) we
dropped the code that made use of those fields but did not remove
the code that sets those fields.

So just remove them to avoid confusion.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/relocation.c

@@ -1384,7 +1384,6 @@ static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans,
 	struct extent_buffer *eb;
 	struct btrfs_root_item *root_item;
 	struct btrfs_key root_key;
-	u64 last_snap = 0;
 	int ret;
 
 	root_item = kmalloc(sizeof(*root_item), GFP_NOFS);
@@ -1401,7 +1400,6 @@ static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans,
 		ret = btrfs_copy_root(trans, root, root->commit_root, &eb,
 				      BTRFS_TREE_RELOC_OBJECTID);
 		BUG_ON(ret);
-		last_snap = btrfs_root_last_snapshot(&root->root_item);
 		/*
 		 * Set the last_snapshot field to the generation of the commit
 		 * root - like this ctree.c:btrfs_block_can_be_shared() behaves
@@ -1435,12 +1433,6 @@ static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans,
 		memset(&root_item->drop_progress, 0,
 		       sizeof(struct btrfs_disk_key));
 		root_item->drop_level = 0;
-		/*
-		 * abuse rtransid, it is safe because it is impossible to
-		 * receive data into a relocation tree.
-		 */
-		btrfs_set_root_rtransid(root_item, last_snap);
-		btrfs_set_root_otransid(root_item, trans->transid);
 	}
 
 	btrfs_tree_unlock(eb);
@@ -2380,9 +2372,6 @@ void merge_reloc_roots(struct reloc_control *rc)
 {
 	struct btrfs_root *root;
 	struct btrfs_root *reloc_root;
-	u64 last_snap;
-	u64 otransid;
-	u64 objectid;
 	LIST_HEAD(reloc_roots);
 	int found = 0;
 	int ret = 0;
@@ -2421,14 +2410,6 @@ again:
 			list_del_init(&reloc_root->root_list);
 		}
 
-		/*
-		 * we keep the old last snapshot transid in rtranid when we
-		 * created the relocation tree.
-		 */
-		last_snap = btrfs_root_rtransid(&reloc_root->root_item);
-		otransid = btrfs_root_otransid(&reloc_root->root_item);
-		objectid = reloc_root->root_key.offset;
-
 		ret = btrfs_drop_snapshot(reloc_root, rc->block_rsv, 0, 1);
 		if (ret < 0) {
 			if (list_empty(&reloc_root->root_list))