Fix variable toolview not sync with framestack view.
Summary:
The problem is caused by the active frame/thread in IVariableController,
which aren't properly updated when autoUpdate() == UpdateNone.
This commit removes m_active{Frame,Thread} because we already only call
update() in the event handler of frame/thread changed event.
Reviewers: kfunk, apol, KDevelop
Reviewed By: apol, KDevelop
Subscribers: mwolff, tcanabrava, apol, kdevelop-devel
Projects: KDevelop
Differential Revision: https://phabricator.kde.org/D1351