Clear out unused tags
https://rbcommons.com/s/pepperdata/r/5049/
Clear the unused tags when we hit /dashboard/tags. There was an existing function that did this, but was never called anywhere. I'm currently calling it when hitting the tags dashboard endpoint. It would be better suited inside the model on a check delete but there seems to be a delay from when the check delete callback is called and the delete actually happens in mongo.