removed Render.clear (redundant)

src/core/Runner.js

@@ -100,7 +100,7 @@ var Runner = {};
             Events.trigger(engine, 'tick', event);
 
             // if world has been modified, clear the render scene graph
-            if (engine.world.isModified)
+            if (engine.world.isModified && engine.render.controller.clear)
                 engine.render.controller.clear(engine.render);
 
             // update

src/render/Render.js

@@ -80,16 +80,6 @@ var Render = {};
         return render;
     };
 
-    /**
-     * Clears the renderer. In this implementation, this is a noop.
-     * @method clear
-     * @param {render} render
-     */
-    Render.clear = function(render) {
-        // nothing required to clear this renderer implentation
-        // if a scene graph is required, clear it here (see RenderPixi.js)
-    };
-
     /**
      * Sets the pixel ratio of the renderer and updates the canvas.
      * To automatically detect the correct ratio, pass the string `'auto'` for `pixelRatio`.