Do not install any package from crowbar_join

We install rubygem-chef with the autoyast profile now.

As to rubygem-ruby-shadow, it's not needed anymore as we fixed the bug
that required it to be installed early. See
https://github.com/crowbar/barclamp-pacemaker/commit/230f2a161ea220d6c1c2d51b438d1419759edbe0