Require Qt 5.9
Summary:
Plasma 5.12 requires Qt 5.9, so also plasma-integration can require Qt 5.9
which removes quite some ifdefs.
Reviewers: Plasma, graesslin
Reviewed By: Plasma, graesslin
Subscribers: graesslin, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D9625