Port away from kglobalsettings

Summary:
This was there only to support notifying kdeinit4, which we no longer
care about.

For KF5 we should be sending the specific call to klauncher
to reparse KProtocolManager, which in one case we seem to
actually miss.

Reviewers: Plasma, apol

Reviewed By: apol

Subscribers: apol, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D25637