Adjust everything to use the new systemd abuild helpers. These generate
the post-install/pre-deinstall and post-upgrade scripts automagically,
and abuild now provides some helpers where it's necessary to finegle
things a bit (e.g. see the pipewire-pulse-systemd subpackage).

Signed-off-by: Caleb Connolly <caleb@postmarketos.org>
Co-authored-by: Clayton Craft <clayton@craftyguy.net>
Part-of: !6334