Deprecate DataEngine related code in Plasma::PluginLoader
With Dataengines going away in KF6 or at least being moved to a plasma-internal porting-aid lib, we can no longer have it as public API in the Plasma::PluginLoader class.
With Dataengines going away in KF6 or at least being moved to a plasma-internal porting-aid lib, we can no longer have it as public API in the Plasma::PluginLoader class.