some doc
cleanup openbsd manual installation + remove unnecessary files

The manual OpenBSD installation is now so old and not needed
anymore.
use rather the stdlib prefix function than the good old regsubst hack
remove anchor dependency - fixed #26

given that all os are using package installation now, we can replace
the anchor with the package dependency. It also caused a dependency
cycle as the anchor was for the whole class and not only the package
installation.
fix #26 - do not manage files of a plugin if it should be absent

The directories are recursively managed and will purge these files
anyway and trigger a proper restart. Like that we can safe a few
resources in our catalog.
remove unnecessary dependencies