Drop old-glib ci test as ubuntu 16.04 is no longer available
Drop old-glib ci test as ubuntu 16.04 is no longer available

As per https://github.com/actions/virtual-environments/issues/3287
the support for ubuntu-16.04 stopped working on september 20:th, so
our CI job stopped starting.

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak