AutoTest: Remove dead entities

Mostly unused functions which where planned to be used or
which have become obsolete due to numerous refactorings.

Change-Id: I1c951ad7902c3180c5cc8d8d6ec2d9fa58693701
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/autotest/itemdatacache.h

@@ -45,7 +45,6 @@ public:
     };
 
     void clear() { m_cache.clear(); }
-    bool isEmpty() const { return m_cache.isEmpty(); }
 
     QVariantMap toSettings(const T &valueToIgnore) const
     {