Remove unused postRender method for scene graph nodes and renderables

include/openspace/scene/scene.h

@@ -85,11 +85,6 @@ public:
      */
     void render(const RenderData& data, RendererTasks& tasks);
 
-    /*
-    * Post-Render visible SceneGraphNodes using the provided camera
-    */
-    void postRender(const RenderData& data);
-
     /*
      * Returns the root SceneGraphNode
      */

include/openspace/scene/scenegraphnode.h

@@ -72,7 +72,6 @@ public:
     void update(const UpdateData& data);
     void evaluate(const Camera* camera, const psc& parentPosition = psc());
     void render(const RenderData& data, RendererTasks& tasks);
-    void postRender(const RenderData& data);
     void updateCamera(Camera* camera) const;
 
     //void addNode(SceneGraphNode* child);