Remove ColorSchemeFilter from KStyle

Summary:
The code is duplciated in plasma-integration. According to the summary of
e47245f96ed1f7decc7209eafe969889579b1c38 when it was added to plasma-integration
it could/should have been removed.

Test Plan: When changing color scheme the titlebar color still changes

Reviewers: Plasma, Frameworks, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D25914