With T204732 and T189808 in place, MediaWiki core has support for undoing and reverting not just revisions with multiple slots, but also revisions with non-editablecontent slots (Multi content in the main slot.revisions), This means that Wikibase no longer has to provide this functionality via SubmitEand also revisions with "non-editable" content in the main slot (such as wikibase entityActionies).
This means that Wikibase most likely no longer needs to provide this functionality via SubmitEntityAction by overriding `undo` https://github.com/wikimedia/Wikibase/blob/master/repo/includes/Actions/SubmitEntityAction.php#L83
It's possible that some extra logic is needed, and this will need to be evaluated when the code is looked at, for example we recently touched this in {T97146}
Notes:
- **"non-editable"**: This means content that is not editable by default in MediaWiki (so anything that is not just text / wikitext for example. Wikibase entities do not allow "direct" editing, only editing via our special APIs.
**Acceptance criteria ⛺✨ :**
[] Reduce the "custom code" in the `SubmitEntityAction::undo` method, making use of what MediaWiki core provides where possible