Fix orientation sensor DBus

Summary:
Firstly, it was completely broken, no-one called registerObject.

Secondly deleting the adaptor doesn't really make sense, you'd still
leave the object valid, only have it broken. Docs of
QDBusAbstractAdaptor do say not to ever delete it manually.

Thirdly we don't need Q_CLASSINFO setting the DBus interface on the
exported item when we use an adaptor.

Test Plan:
Manually added some setEnabled/disabled
Could now see the path

Reviewers: KWin

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D23610