PSP improperly handles membership delete from changelog when a group is deleted

When a group is deleted, memberships are first deleted & then the group is deleted in the changelog. The issue though is member delete doesn't contain the groupName in the changelog. When the PSP tries to resolve the appropriate group it fails because the group no longer exists (was deleted).

From Shilen:
The change log has never had subjectName on a membership delete entry. We
can add it there or the PSP can get the subject's name (assuming the
subject is a group) from point in time.