btrfs: remove trans_handle->root

Nobody is using this anymore, remove it.

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/transaction.c

@@ -698,7 +698,6 @@ again:
 
 	h->transid = cur_trans->transid;
 	h->transaction = cur_trans;
-	h->root = root;
 	refcount_set(&h->use_count, 1);
 	h->fs_info = root->fs_info;
 

fs/btrfs/transaction.h

@@ -135,7 +135,6 @@ struct btrfs_trans_handle {
 	bool removing_chunk;
 	bool reloc_reserved;
 	bool in_fsync;
-	struct btrfs_root *root;
 	struct btrfs_fs_info *fs_info;
 	struct list_head new_bgs;
 };