Avoid needless config parse

Summary:
There's practically no reason to ever open kdeglobals. The way the kde
cascading configuration system works is that we'll have those settings
included in our plasmashellrc which we've already loaded.

Not only is it faster but we also honour any kdeglobals setting
overrides from /etc/ .

Test Plan:
Changed setting in kdeglobals
Setting still applied

Reviewers: Plasma, hein, apol

Reviewed By: apol

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D16384