Deprecate defunct functions

Summary:
As in T12163 explained KRunner should be ported away from QWidgets and the
fuctions are defuct anyway.

Test Plan: Compiles

Reviewers: Plasma, broulik, davidedmundson, vkrause, meven

Reviewed By: meven

Subscribers: kossebau, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D29281