desktoppackage: Fix relaying configuration change signals
Fixes no-so-verbose-as-I'd-like-them-to-be errors from QML/JS Engine:
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/configTimeZones.qml:254:
Error: Unable to determine callable overload. Candidates are:
Yes, it does not print any candidates, let alone mentioning the object itself and the name of a signal which wasn't found.
The correct way it to pass a closure (function) to connect() calls, because only that way JavaScript can preserve binding between an object and its method. See Function.prototype.bind() for an alternative approach and in-depth description of this problem.