Provide a cleanup method for old, legacy or pre-8.9 artifacts

Hi while reading this and wondering what happens to my 24GB old artifacts i was searching for a default behaviour, it's documented here: http://docs.gitlab.com/ce/ci/yaml/README.html#artifactsexpire_in.

When are pre-8.9 created artifacts beeing deleted? Do they have an expiry date or would it make sense to add a rake task which can set a default expire or cleanup artifacts.