GenericProposalWidget: Delete old code for carbon qt

Change-Id: Ib8cc14764a3ff590e74c581792562ee8ead969b1
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
TaskHub: Sanitize tasks and reject obviously invalid ones.

I hope this helps to track down tasks as described in QTCREATORBUG-11976

Change-Id: I758c28c56ad69aa0c19896065925de188475bda3
Reviewed-by: Daniel Teske <daniel.teske@digia.com>