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

ui/aura/client/focus_client.h

Index: ui/aura/client/focus_client.h
diff --git a/ui/aura/client/focus_client.h b/ui/aura/client/focus_client.h
index f084349705c3e2c7f37d7e51f1e268c3bd572bea..cec64ec6ddb84d72b5094b1c7c31d2053137f65c 100644
--- a/ui/aura/client/focus_client.h
+++ b/ui/aura/client/focus_client.h
@@ -6,7 +6,10 @@
 #define UI_AURA_CLIENT_FOCUS_CLIENT_H_
 
 #include "ui/aura/aura_export.h"
-#include "ui/aura/window.h"
+
+namespace ui {
+class Event;
+}
 
 namespace aura {
 class Window;
@@ -37,9 +40,6 @@
 AURA_EXPORT FocusClient* GetFocusClient(Window* window);
 AURA_EXPORT FocusClient* GetFocusClient(const Window* window);
 
-// The focus client is stored on the window using this property.
-AURA_EXPORT extern const WindowProperty<FocusClient*>* const kFocusClientKey;
-
 }  // namespace clients
 }  // namespace aura