d-f-s: Delete volumes

Previously we were assuming that every volume would be referenced by a container. However, gitlab-runner has now changed to deleting its transient containers and looking up the volume name directly, based on the runner ID and a hash value for the repository.

As not having the container history means that we no longer have an LRU, just delete volumes based on their creation date. This gives us fewer cache hits for the Git repository clone, however we now have the infrastructure to handle clones through a local MinIO cache.