Sometimes a review will be made of an entity which is then deleted from musicbrainz (not merged). When this happens, we try to show a placeholder with [Unknown] as a title, however this isn't always easy to get right

Specifically in this example, we're missing [unknown] for the artist credit, and there is still a "write a review" button and a call to add a spotify link. If we want to continue showing reviews for deleted items, we should hide these items.

https://www.critiquebrainz.org/release-group/e623e122-323b-4637-bd4b-f6950ecf2dff

Some ideas about how we could improve this:

• Add a notification that says that this item has been deleted from MusicBrainz
• Add an admin report that shows items that have been deleted
• Somehow notify users that an entity has been deleted, and see if there's an option to change its mbid to another item that exists?
• Store the name/title of entities in the review table, this would allow us to show them even if the item is deleted from musicbrainz
• It's also possible that reviews that fall into this category are spam, and we should have a way of checking this and removing them if necessary