Core: Use some data members in NavigationWidgetFactory

Adjust user code, remove unused bits.

Change-Id: I351deb27679c9251518a4d1bf7f78a12bacae2fb
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/classview/classviewplugin.cpp

@@ -51,11 +51,8 @@ bool Plugin::initialize(const QStringList &arguments, QString *errorMessage)
     Q_UNUSED(arguments)
     Q_UNUSED(errorMessage)
 
-    // create a navigation widget factory
-    (void) new NavigationWidgetFactory;
-
     // add to ExtensionSystem
-    addAutoReleasedObject(NavigationWidgetFactory::instance());
+    addAutoReleasedObject(new NavigationWidgetFactory);
 
     // create manager
     (void) new Manager(this);