fix for expire not expiring old entries

[Richard Todd]

When group-based-expire is on, expire never removes history entries
for "old" entries for expired articles (the 2-field entries). This
is because with group-based-expire on, expire never reads expire.ctl.
This patch reenables expire's reading of expire.ctl, and makes it just
ignore the entries in there for per-group expire (since the actual
removal of articles is done by expireover and friends).