Up until now, it has been Attic policy to request removal of the LDAP groups relating to projects that have moved to the Attic. I think the same is true of podlings.
However when I requested deletion of Oltu groups, I was told that it was now policy not to remove obsolete groups [1] I'm hopeful that policy can be reversed. There are various places where LDAP group memberships are listed, and it will be confusing to show an ever increasing number of obsolete groups. S. [1] https://issues.apache.org/jira/browse/INFRA-17784?focusedCommentId=16756864&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16756864
