Remove pointless Debian support to simplify code

Packstack is incompatible to Debian in many places, therefore
supporting it in just one single place just makes no sense. If
at all, complete instead of very partial Debian support should
be introduced. Until such time it's easiest to support all the
different Fedora and RHEL derivatives by having no operating
system discriminator at all.

Partially discussed at:
https://bugzilla.redhat.com/show_bug.cgi?id=906269

Change-Id: I93cd4d25b0f85bae24c97be6ed91547dce1935d7