The feature was part of the old role but unconditionally. When porting
to external role we made it optional with variable
`docker_cron_image_prune` but default to false. Restore the previous
behaviour in this playbook.
We used a similar local role here, in the Freifunk Magdeburg project,
and in personal playbooks. That was moved to an external project,
unified, and reworked, so the external role can act as replacement for
the distributed, redundant copies.
Link: https://github.com/netz39/ansible-role-host-docker
Fixes the following ansible-lint warnings:
yaml[comments]: Too few spaces before comment
host-unicorn.yml:31
yaml[comments]: Too few spaces before comment
host-wittgenstein.yml:143
