Fix annoying warning
Summary:
Warning for every plugin was:
The file includes the moc file "generator_tiff.moc", but does not contain a Q_OBJECT, Q_GADGET, Q_NAMESPACE, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON or K_PLUGIN_FACTORY macro.
Test Plan: Built
Reviewers: aacid
Reviewed By: aacid
Subscribers: Okular
Tags: Okular
Differential Revision: https://phabricator.kde.org/D10022