remove dangling remote widgets code
Summary:
can't be enabled anywhere + not actually doing anything as there is no
backing for it in the cpp + qca isn't even looked for by cmake
Test Plan: none
Reviewers: Plasma, broulik
Reviewed By: Plasma, broulik
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D22618