[Sync] Remove unneeded 'using syncer::' lines and 'syncer::' scopings

sync/notifier/invalidation_util.h

Index: sync/notifier/invalidation_util.h
diff --git a/sync/notifier/invalidation_util.h b/sync/notifier/invalidation_util.h
index 55de45487ba06e958dc85b210d0da009068d8268..1a706efb67f0c6d35cfa1630b3c0d83312f168fa 100644
--- a/sync/notifier/invalidation_util.h
+++ b/sync/notifier/invalidation_util.h
@@ -28,11 +28,11 @@ struct ObjectIdLessThan {
 
 typedef std::set<invalidation::ObjectId, ObjectIdLessThan> ObjectIdSet;
 
-bool RealModelTypeToObjectId(syncer::ModelType model_type,
+bool RealModelTypeToObjectId(ModelType model_type,
                              invalidation::ObjectId* object_id);
 
 bool ObjectIdToRealModelType(const invalidation::ObjectId& object_id,
-                             syncer::ModelType* model_type);
+                             ModelType* model_type);
 
 std::string ObjectIdToString(const invalidation::ObjectId& object_id);