You also need to walk through the database and delete any attributes
object classes defined by the overlay. That'll be at least any
operational attributes since they must be hardcoded into the C source.
Er - might be easer for the manager to do this (maybe with help from the
overlay) so the overlay merely needs to check if the database is in a
state where the overlay can be deleted. Might not be possible with all
overlays though, if an entry with no attributes from the overlay would
be invalid as far as the overlay is concerned.