Correctly deinitialize scenegraph nodes that are added at runtime

include/openspace/scene/scene.h

@@ -84,12 +84,6 @@ public:
     Scene(std::unique_ptr<SceneInitializer> initializer);
     virtual ~Scene() override;
 
-    /**
-     * Clear the scene graph,
-     * i.e. set the root node to nullptr and deallocate all scene graph nodes.
-     */
-    void clear();
-
     /**
      * Attach node to the root
      */