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

ui/views/mus/mus_client.cc

Index: ui/views/mus/mus_client.cc
diff --git a/ui/views/mus/mus_client.cc b/ui/views/mus/mus_client.cc
index 2a73231972a333202e7dd245ed9ec78d49577652..399094d899ebdb46dd673f78763586242c5a182d 100644
--- a/ui/views/mus/mus_client.cc
+++ b/ui/views/mus/mus_client.cc
@@ -249,10 +249,6 @@ void MusClient::OnWindowManagerFrameValuesChanged() {
     observer.OnWindowManagerFrameValuesChanged();
 }
 
-aura::client::CaptureClient* MusClient::GetCaptureClient() {
-  return wm::CaptureController::Get();
-}
-
 aura::PropertyConverter* MusClient::GetPropertyConverter() {
   return property_converter_.get();
 }