prune_objects can prune orphaned activities who reference an array of objects

prune_objects can prune orphaned activities who reference an array of objects

E.g. Flag activities have an array of objects

We prune the activity when NONE of the objects can be found

Note that the cost of finding and deleting these is ~4x higher than finding and deleting the non-array ones

Only string:
Delete on activities  (cost=506573.48..506580.38 rows=0 width=0)

Only Array:
Delete on activities  (cost=3570359.68..4276365.34 rows=0 width=0)

(They are still executed separately, so the total cost is the sum of the two)