Exclude powerdevil from session management
Summary:
I found this process in my ksmserverrc
This is autostarted through other ways, and there's no useful data that
should persist across sessions.
Test Plan: Code is copy pasted
Reviewers: Plasma, broulik
Reviewed By: Plasma, broulik
Subscribers: broulik, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D19024