[kcm/standardactions] Don't register kcminit hook when we don't have one
There is no exported function called standard_actions. kcminit will link
against this library, fail to find a method to run and do nothing.
Test Plan: Grepped for method
Reviewers: Plasma, broulik
Reviewed By: Plasma, broulik
Differential Revision: https://phabricator.kde.org/D27007