Don't start ksmserver with lockscreen integration on wayland

Summary:
Fixes regression from the startkde C++ re-write which made ksmserver
start the kscreenlocker in wayland session, resulting in the double
lockscreeens.

Test Plan: after applying patch I only get one lockscreen

Reviewers: apol

Reviewed By: apol

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D22021