fix analyzer error in path observer test

pkg/mdv_observe/test/path_observer_test.dart

Index: pkg/mdv_observe/test/path_observer_test.dart
diff --git a/pkg/mdv_observe/test/path_observer_test.dart b/pkg/mdv_observe/test/path_observer_test.dart
index ef62025d51fa43b7b8850322ed448b990a1e007d..4222f73f109b516a10c6fa1cc2fef8271e1ead20 100644
--- a/pkg/mdv_observe/test/path_observer_test.dart
+++ b/pkg/mdv_observe/test/path_observer_test.dart
@@ -247,6 +247,3 @@ class TestModel extends ObservableBase {
 
   toString() => '#<$runtimeType $fieldName: $_value>';
 }
-
-_record(key, oldValue, newValue, [kind = ChangeRecord.FIELD]) =>
-    new ChangeRecord(key, oldValue, newValue, kind: kind);