Get rid of Deleted's properties

Summary:
EffectWindow no longer looks up properties from Toplevel derived
classes, thus we can get rid of Deleted's properties. It's safe to do
because Deleted is not exposed to scripting API and those properties
were used only by effects.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D19722