Mojo C++ bindings: remove some usage of AssociatedGroup from user code.

services/ui/ws/test_server_window_delegate.cc

Index: services/ui/ws/test_server_window_delegate.cc
diff --git a/services/ui/ws/test_server_window_delegate.cc b/services/ui/ws/test_server_window_delegate.cc
index 0242fed06ed5b686600eded676d4e7230c4cbc23..32cd20306e37cc1e20cb9fe3c016de71f7d947fa 100644
--- a/services/ui/ws/test_server_window_delegate.cc
+++ b/services/ui/ws/test_server_window_delegate.cc
@@ -17,11 +17,6 @@ cc::mojom::DisplayCompositor* TestServerWindowDelegate::GetDisplayCompositor() {
   return nullptr;
 }
 
-mojo::AssociatedGroup*
-TestServerWindowDelegate::GetDisplayCompositorAssociatedGroup() {
-  return nullptr;
-}
-
 ServerWindow* TestServerWindowDelegate::GetRootWindow(
     const ServerWindow* window) {
   return root_window_;