Clean up old bug workaround

Summary:
The workaround is not necessary anymore.
See https://bugreports.qt.io/browse/QTBUG-40765
See also D22012

Test Plan: Manually tested

Reviewers: davidedmundson, Plasma

Reviewed By: davidedmundson, Plasma

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D23175