Remove traces of old GTK configs
Summary:
Since slider behavior is controlled by kded daemon, gtk kcm has no control over it now.
It appears, that some traces of the warps-slider config were not removed. Now it is removed along with some other ones redundant lines.
Test Plan: Check that GTK KCM no longer crash, if entered from System Settings.
Reviewers: ngraham
Reviewed By: ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D25863