Don't use KPluginInfo if we can use KPluginMetaData
Summary: KPluginInfo would force the load of the desktop file for information we don't need.
Test Plan: Plasma still works
Reviewers: Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22480