Fix analyzer warning

Author: daohoangson

packages/core/test/_.dart

@@ -607,16 +607,15 @@ class Explainer {
       return _widget(widget.builder(context));
     }
 
-    if (widget is LayoutBuilder ||
-        widget.runtimeType.toString() == 'HtmlLayoutBuilder') {
+    if (widget is LayoutBuilder) {
       return _widget(
-        (widget as dynamic).builder(
+        widget.builder(
           context,
           BoxConstraints.loose(
             TestWidgetsFlutterBinding
                 .instance.platformDispatcher.implicitView!.physicalSize,
           ),
-        ) as Widget,
+        ),
       );
     }