Previously, we'd forward org.freedesktop.DBus.Local.Disconnected like
any other message to the other side. But that's not OK, as messages in
the org.freedesktop.DBus.Local.* namespace are supposed to never touch
the wire, and are synthetic messages that the library uses to
communicate with the app, but never with other apps.
dbus-daemon never cared, but dbus-broker complains about this, hence
clean this up.
See: #28514
Lennart Poettering
0321248b79