Unnecessary new (#20138)

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests
diff --git a/examples/layers/rendering/hello_world.dart b/examples/layers/rendering/hello_world.dart
index 8480158..1f49ca7 100644
--- a/examples/layers/rendering/hello_world.dart
+++ b/examples/layers/rendering/hello_world.dart
@@ -9,14 +9,14 @@
 
 void main() {
   // We use RenderingFlutterBinding to attach the render tree to the window.
-  new RenderingFlutterBinding(
+  RenderingFlutterBinding(
     // The root of our render tree is a RenderPositionedBox, which centers its
     // child both vertically and horizontally.
-    root: new RenderPositionedBox(
+    root: RenderPositionedBox(
       alignment: Alignment.center,
       // We use a RenderParagraph to display the text 'Hello, world.' without
       // any explicit styling.
-      child: new RenderParagraph(
+      child: RenderParagraph(
         const TextSpan(text: 'Hello, world.'),
         // The text is in English so we specify the text direction as
         // left-to-right. If the text had been in Hebrew or Arabic, we would