This patch changes the behaviour to be thus:

- If the artefact now has no parent, we can safely remove all records in the APC
- If it does have a parent, insert a non-dirty record representing that relationship
- Mark all other rows referencing the artefact as dirty - we can't make any more conclusions at this point.

The cronjob will come through and clean up the dirty rows, as it always has done.
(cherry picked from commit bdca8220ebddf155bffa26c34f48c5795a774e0b)