With the upgrade to Varnish 5 being completed (T168529), we now need to perform some post-upgrade cleanups (similarly to what we did in T150660 for the v3->v4 migration) including:
- moving all v5 packages from experimental to main on apt.w.o
- removing v4/v5 conditionals in VCL templating
- getting rid of puppet conditionals based on profile::cache::base::varnish_version