remove LazyUnnamedSection* from pkgcore.config.*

Those sets of classes came in for dhcp style config, which is long since dead.  They're used by `convert_asis` in a way that shouldn't work; they invoke `collapse_section([stack])` without passing a name, which doesn't align w/ polymorphic requirements.

Beyond that, it just doesn't particularly make sense anymore.  Isolate fully why it's there and then remove it or update the notes for it.