We should not delete flaggings on account cancelation

Over four years onward, I needed a more nuanced implementation, here's a stab at it. This only deletes flaggings when re-assigning content to the anonymous user (deleting a user will already call the existing pre-delete hook). Also, it checks the number of flaggings to remove to a threshold, and will create a queue to delete the flaggings in batches when it exceeds the threshold. The threshold itself is obviously up for debate, maybe the current 20 is a bit too convervative.

Can you elaborate on the reason this needs work? AFAICT the merge request is mergeable.

Sorry, I took your message #8 as meaning that the MR needs some work.

Also, needs tests

Ah, no, it was meant to say I adjusted the MR. Fair enough to get some tests.