net-vpn/networkmanager-sstp: disable libnm-glib usage, fix some deps

net-vpn/networkmanager-sstp: disable libnm-glib usage, fix some deps

* Ensure libnm-glib and co usage is always disabled
* Fix USE=gtk deps; libnma was missing, even after --without-libnm-glib
* Add missing gdbus-codegen build dep
* Drop dbus-glib dep, long ported to GDBus; dep on needed minimum glib
  as per upstream
* Drop ltprune.eclass usage and unused eutils.eclass inherit
* Other small min dep tweaks per configure.ac

Package-Manager: Portage-2.3.84, Repoman-2.3.20
Signed-off-by: Mart Raudsepp <leio@gentoo.org>