Notifies the subscriber after "Check - Empty Cards" removed cards

[Arthur-Milchior]

See #16941 for the details. This issue can be closed specifically when, after a "Check cards" ends by deleting cards, ChangeManager.notifySubscribers is called with a OpChanges where all at least card, browser_table, study_queues are set to true

[david-allison]

This seems like a good one to tackle with a my backup PC this weekend

[david-allison]

Anki backend currently does not support this.

Added:

https://forums.ankiweb.net/t/removecards-should-return-opchangeswithcount/48597

[Arthur-Milchior]

ankitects/anki#3386 ensured that "empty card" is cancellable. Once the back-end is updated in ankidroid, we can use this feature directly