deletes must use top level dt as event time

Deletes were receiving the timestamp of the revision. In cases where a page is edited and then deleted (quite common) both events had the same event time. When that goes to DeduplicateAndMerge the sort is arbitrary, since both events match on all fields. The delete of a revision should always come after the creation of a revision though.

To resolve use the time the event was created as the delete event time. This should ensure the deletion of a revision is prioritized over the edit that created the revision.