Revert of Improves focus/activation for aura-mus and DesktopNativeWidgetAura

ui/aura/env_observer.h

Index: ui/aura/env_observer.h
diff --git a/ui/aura/env_observer.h b/ui/aura/env_observer.h
index 274bf3f4bc48ac04561a4bc2b8dadca7c652d8f4..03fcf3bd171e3291bf310b5dd6630470a337b07a 100644
--- a/ui/aura/env_observer.h
+++ b/ui/aura/env_observer.h
@@ -11,10 +11,6 @@
 
 class Window;
 class WindowTreeHost;
-
-namespace client {
-class FocusClient;
-}
 
 class AURA_EXPORT EnvObserver {
  public:
@@ -30,10 +26,6 @@
   // Called right before Env is destroyed.
   virtual void OnWillDestroyEnv() {}
 
-  // Called from Env::SetActiveFocusClient(), see it for details.
-  virtual void OnActiveFocusClientChanged(client::FocusClient* focus_client,
-                                          Window* window) {}
-
  protected:
   virtual ~EnvObserver() {}
 };