btrfs: Remove stale comment about select_delayed_ref

select_delayed_ref really just gets the next delayed ref which has to
be processed - either an add ref or drop ref. We never go back for
anything. So the comment is actually bogus, just remove it.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -2705,10 +2705,6 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
 		spin_lock(&locked_ref->lock);
 		btrfs_merge_delayed_refs(trans, delayed_refs, locked_ref);
 
-		/*
-		 * locked_ref is the head node, so we have to go one
-		 * node back for any delayed ref updates
-		 */
 		ref = select_delayed_ref(locked_ref);
 
 		if (ref && ref->seq &&