[kcm] Drop 'Enable bluetooth integration' setting

Summary: It controls whether the bluedevil kded module is loaded. I don't see any use case for it. If one really really needs to disable the kded module this can be done from the kded KCM.

Reviewers: #plasma, drosca

Reviewed By: drosca

Subscribers: broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D27572