classifier: Make classifier_for_each() easier to use.

classifier: Make classifier_for_each() easier to use.

classifier_for_each() and classifier_for_each_match() previously had the
restriction that the callback could not delete any rule that would be
visited in the same call, even if it was in a different table (except for
the rule actually passed to the callback).  But a number of callers do
want to delete rules in other tables, and it is easy to eliminate that
restriction, so this commit does so.