Right now if we re-export a dashboard and an old chart is no longer on it, that chart will live forever in a live system unless the operator manually deletes it. I think we can have a way to remove known-orphaned charts or dashboards by having a file that tracks all IDs that have been released and then subsequently orphaned. I think we'd have to maintain this manually, but it's easy to add ids that have been missed.

I'm thinking a yaml file that just stores a dict of types (dashboard, chart, etc) and a small script that loops through them and calls the API to delete them, similar to how we do import. It can eat errors if the id already doesn't exist.