D-Bus 1.3.1 (2010) introduced the standard "PropertiesChanged" signal
on "org.freedesktop.DBus.Properties". NetworkManager is old, and predates
this API. From that time, it still had it's own PropertiesChanged signal
that are emitted together with the standard ones. NetworkManager
supports the standard PropertiesChanged signal since it switched to
gdbus library in version 1.2.0 (2016).
These own signals are deprecated for a long time already ([1], 2016), and
are hopefully not used by anybody anymore. libnm-glib was using them and
relied on them, but that library is gone. libnm does not use them and neither
does plasma-nm.
Hopefully no users are left that are affected by this API break.
[1] 6fb917178a
This property is currently most likely not used. Also, because libnm doesn't
expose it and the only known user of this API (gnome-network-displays) doesn't
use it.
In the future we may want to expand on the Groups API. E.g. exposing groups as
separate D-Bus objects, in which case a better property type would be "ao" and
not "as". For now, that is unclear nor requested.
Remove the property for now.
