It is mosty unused, except for two places:
- Some stuff in Amarok has `X-KDE-PluginInfo-Depends=Amarok2.0`
- https://invent.kde.org/plasma/plasma-sdk/-/blob/master/themeexplorer/src/thememodel.cpp#L303
In both cases I'm not even sure it does anything useful
KPluginSelector has quite a bit of code that handles dependencies. Getting rid of that complexity would help with T12265