Remove WindowTreeClientDelegate::GetCaptureClient() and WindowTreeClient::GetCaptureClient().

services/ui/demo/mus_demo.cc

Index: services/ui/demo/mus_demo.cc
diff --git a/services/ui/demo/mus_demo.cc b/services/ui/demo/mus_demo.cc
index 0ae145c089fcc1878d5d867fd31b48437151a9c0..0fbcd356c25475ef3794f4687541853891d9582f 100644
--- a/services/ui/demo/mus_demo.cc
+++ b/services/ui/demo/mus_demo.cc
@@ -118,10 +118,6 @@ void MusDemo::OnLostConnection(aura::WindowTreeClient* client) {
 void MusDemo::OnPointerEventObserved(const PointerEvent& event,
                                      aura::Window* target) {}
 
-aura::client::CaptureClient* MusDemo::GetCaptureClient() {
-  return capture_client_.get();
-}
-
 aura::PropertyConverter* MusDemo::GetPropertyConverter() {
   return property_converter_.get();
 }