bind9 purging?

In class site_config::resolvconf there is the following

  # bind9 purging can be taken out after some time
  package { 'bind9':
    ensure => absent,
  }
  file { '/etc/default/bind9':
    ensure    => absent;
  }
  file { '/etc/bind/named.conf.options':
    ensure => absent;
  }

Can you explain why bind9 is being purged here and what is necessary to do so we can satisfy the comment?

(from redmine: created on 2013-06-13, closed on 2013-07-02, relates #8213 (closed))