deletion collector: only call pre/post_deleted if not auto_created
deletion collector: only call pre/post_deleted if not auto_created

This follows Django's way of doing it for non-versionable objects.

swisscom/cleanerversion,anfema/cleanerversion,swisscom/cleanerversion,swisscom/cleanerversion,pretix/cleanerversion,anfema/cleanerversion,anfema/cleanerversion,pretix/cleanerversion,pretix/cleanerversion