Fix a memory leak in KuitStaticData

Summary:
domainSetups QHash was populated in Kuit::setupForDomain, but
the values of the QHash where not deleted in the default destructor.
All the credit goes to mpyne, anthonyfierony, aacid and apol.

Reviewers: Frameworks, dfaure

Reviewed By: dfaure

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D9156