dbus: Drop support for older (3 years +) Qt versions

The Trolltech namespace is deprecated since 2008,
the digia and nokia namespaces replaced them in
2008-2011 then it was moved to the Qt project itself

The trolltech namespace was kept to avoid the 3
successive renames from 2008-2011. It would have
caused issues for some LTS distributions. It is no
longer an issue.

Refs #50191

Change-Id: Ic1457ea00b6decbfc875aa671af97effd1be09d3