[ksmserver] Remove blocking call introspecting KDED
Summary:
We don't need to introspect at runtime as KDED installs the interface
XML file.
Oddly KDED's package is called KDED not KF5KDED, hence the separate
find_package, I don't know if that's a bug in frameworks or not.
Test Plan: Compiles
Reviewers: Plasma, romangg
Reviewed By: Plasma, romangg
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D16628