[kded] Clean up notification handling
Summary:
Remove calls to deleteLater(), KNotification objects delete themselves after they timed out.
Remove unnecessary parent assignments.
Remove unnecessary id check before storing, this was introduced in a19794a3e as a supposed crash fix, but I doubt it actually fixes anything.
Test Plan: Spawned some connection (de)activated and error notifications
Reviewers: jgrulich, Plasma, broulik
Reviewed By: jgrulich
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D28691