Remove unrelated code to make sure oxygen font is installed

Summary:
Relevant code is already removed from startkde, remove it from plasma
wayland session as well

Test Plan: none

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: davidedmundson, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D21426