Revert "Enqueue superclasses instead of supertypes."

pkg/compiler/lib/src/common/backend_api.dart

Index: pkg/compiler/lib/src/common/backend_api.dart
diff --git a/pkg/compiler/lib/src/common/backend_api.dart b/pkg/compiler/lib/src/common/backend_api.dart
index b095b230809e7c65cb78c1e79b78df1a36adc1e8..71c86165d11cd1d5fea54d9666e27735e3153c70 100644
--- a/pkg/compiler/lib/src/common/backend_api.dart
+++ b/pkg/compiler/lib/src/common/backend_api.dart
@@ -153,12 +153,6 @@ abstract class Backend {
                                  Enqueuer enqueuer,
                                  Registry registry) {}
 
-  /// Called to notify to the backend that a class is implemented by an
-  /// instantiated class.
-  void registerImplementedClass(ClassElement cls,
-                                Enqueuer enqueuer,
-                                Registry registry) {}
-
   /// Called to notify to the backend that an interface type has been
   /// instantiated.
   void registerInstantiatedType(InterfaceType type, Registry registry) {}