This led to an infinite recursion in case the annotation was completely
missing. Instead of trying to fix that, I'm simply implementing the
"### Qt6" request from c62f717226 .
[ChangeLog][qdbusxml2cpp] Removed the old compatibility code that
accepted "In" annotations for signal argument names, introduced in Qt
5.8.
Pick-to: 6.4
Fixes: QTBUG-104722
Change-Id: Ie4bb662dcb274440ab8bfffd1709bfc3daf0846d
Reviewed-by: David Faure <david.faure@kdab.com>