Don't block all the ksmserver process when calling kded.loadSecondPhase

Summary:
It's an overly slow call and it gets in the way on a process that needs
to be responsive

Test Plan: Still boots

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: davidedmundson, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D9090