Core: add ICore::isQtDesignStudio()

Change-Id: I3aed97b62abd05b283ac327be210af75f173383d
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmlprojectmanager/qmlproject.h

@@ -17,7 +17,6 @@ class QMLPROJECTMANAGER_EXPORT QmlProject : public ProjectExplorer::Project
 public:
     explicit QmlProject(const Utils::FilePath &filename);
 
-    static bool isQtDesignStudio();
     static bool isQtDesignStudioStartedFromQtC();
     bool isEditModePreferred() const override;