All of the group, host and container mapping per service that
it used to do has since been refactored into per-service files
in the etc/openstack_deploy/env.d directory.
Removing this file, the accompanying documentation and the
logic within the dynamic inventory script should help remove
some complexity for deployers and project maintainers.
Change-Id: Ie8bedca2ca047ebddac32189e85cb201601d068c