Revert of [Sync] Make directory types registration explicit in ModelTypeRegistry

components/sync/driver/model_type_controller_unittest.cc

Index: components/sync/driver/model_type_controller_unittest.cc
diff --git a/components/sync/driver/model_type_controller_unittest.cc b/components/sync/driver/model_type_controller_unittest.cc
index 1de837054c52d6896235d5cef477b044ed8e2ca7..bf7ef71eb664908c0fb96e42e80d03b9070378d9 100644
--- a/components/sync/driver/model_type_controller_unittest.cc
+++ b/components/sync/driver/model_type_controller_unittest.cc
@@ -92,15 +92,6 @@
     NOTREACHED() << "Not implemented.";
   }
 
-  void RegisterDirectoryDataType(ModelType type,
-                                 ModelSafeGroup group) override {
-    NOTREACHED() << "Not implemented.";
-  }
-
-  void UnregisterDirectoryDataType(ModelType type) override {
-    NOTREACHED() << "Not implemented.";
-  }
-
   void ActivateDirectoryDataType(ModelType type,
                                  ModelSafeGroup group,
                                  ChangeProcessor* change_processor) override {