Allow sync *, async * and yield * in dart2js

pkg/compiler/lib/src/warnings.dart

Index: pkg/compiler/lib/src/warnings.dart
diff --git a/pkg/compiler/lib/src/warnings.dart b/pkg/compiler/lib/src/warnings.dart
index e21429c46346cbccfba867f8106dff3440493b2a..89e69e9f2ed28fc399e1090e10995287ac88d38b 100644
--- a/pkg/compiler/lib/src/warnings.dart
+++ b/pkg/compiler/lib/src/warnings.dart
@@ -2078,16 +2078,6 @@ Please include the following information:
   static const MessageKind EXPERIMENTAL_ASYNC_AWAIT = const MessageKind(
       "Experimental language feature 'async/await' is not supported.");
 
-  static const MessageKind INVALID_STARRED_KEYWORD = const MessageKind(
-      "Invalid '#{keyword}' keyword.",
-      options: const ['--enable-async'],
-      howToFix: "Try removing whitespace between '#{keyword}' and '*'.",
-      examples: const [
-        "main() async * {}",
-        "main() sync * {}",
-        "main() async* { yield * null; }"
-      ]);
-
   static const MessageKind INVALID_SYNC_MODIFIER = const MessageKind(
       "Invalid modifier 'sync'.",
       options: const ['--enable-async'],