Faster update by speeding up repair step "Remove activity entries of private events"

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Is your feature request related to a problem? Please describe.
When running an update of our Nextcloud Instance (or occ maintenance:repair) I face a very intense slowdown (>30 min) on the repair step Remove activity entries of private events. oc_activity contains 312.577 entries and this does not seam to be very very much because I already searched a bit in the Nextcloud Forum.
It would be great if this step could be more fast.

Describe the solution you'd like
I tired to understand what happens on this step and it seams to me that https://github.com/nextcloud/server/blob/01b2ae4e4e47a58e3036184bbd52d8fdd76ee412/apps/dav/lib/Migration/RemoveClassifiedEventActivity.php#L48 for every calendar entry of every user is trying to delete lines in oc_activity that in column affecteduser have something different than the user that is the owner of the calendar entry.
I asked myself if it wouldn't be possible to simply delete every entry of this type without having to do this in a while loop one by one? I may be wrong (very probably 😉) but couldn't we delete every entry in oc_activity that has an other value in affecteduser than in owner?

Say:

		$delete->delete('activity')
			->where($delete->expr()->neq('affecteduser', $delete->createParameter('owner')))
                        ->andWhere($delete->expr()->eq('owner', $delete->createParameter('owner')))
			->andWhere($delete->expr()->eq('object_type', $delete->createParameter('type')))
			->andWhere($delete->expr()->eq('object_id', $delete->createParameter('calendar_id')));

Start with apps/dav/lib/Migration/RemoveClassifiedEventActivity.php at the linked repair step, then run occ maintenance:repair against the described activity data to understand the current behavior. Compare a set-based deletion with the existing per-calendar processing, and consider the work done when private-event activity entries are removed correctly without the reported slowdown.