Revert 154611 - "Forget about DesktopBackgroundView if it was deleted"

ash/desktop_background/desktop_background_controller.h

Index: ash/desktop_background/desktop_background_controller.h
diff --git a/ash/desktop_background/desktop_background_controller.h b/ash/desktop_background/desktop_background_controller.h
index 71eb8ff917af0f767aea3b01691fbcd53e8a43c3..0251c1c8d4e84af333c2458976a2847cf56f85b9 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -125,10 +125,6 @@ class ASH_EXPORT DesktopBackgroundController : public aura::WindowObserver {
   // Move all desktop widgets to unlocked container.
   void MoveDesktopToUnlockedContainer();
 
-  // Drop references to background view for |root_window|, because the view
-  // was deleted.
-  void CleanupView(aura::RootWindow* root_window);
-
   // WindowObserver implementation.
   virtual void OnWindowDestroying(aura::Window* window) OVERRIDE;