Unnecessary new (#20138)

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests
diff --git a/packages/flutter_tools/test/config_test.dart b/packages/flutter_tools/test/config_test.dart
index 30edb71..63e1d71 100644
--- a/packages/flutter_tools/test/config_test.dart
+++ b/packages/flutter_tools/test/config_test.dart
@@ -14,7 +14,7 @@
   setUp(() {
     tempDir = fs.systemTempDirectory.createTempSync('flutter_config_test.');
     final File file = fs.file(fs.path.join(tempDir.path, '.settings'));
-    config = new Config(file);
+    config = Config(file);
   });
 
   tearDown(() {