Remove support for the DeferredLibrary annotation and remove tests of it

tests/compiler/dart2js_extra/deferred/deferred_constant4_test.dart

Index: tests/compiler/dart2js_extra/deferred/deferred_constant4_test.dart
diff --git a/tests/compiler/dart2js_extra/deferred/deferred_constant4_test.dart b/tests/compiler/dart2js_extra/deferred/deferred_constant4_test.dart
index ee4b0d6fe3bd5383ae64553433af5752ecb1e74d..af903f48f56b68204eb292df1b03134e151fe73b 100644
--- a/tests/compiler/dart2js_extra/deferred/deferred_constant4_test.dart
+++ b/tests/compiler/dart2js_extra/deferred/deferred_constant4_test.dart
@@ -5,15 +5,11 @@
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 
-import 'dart:async';
-
-@lazy import 'deferred_class_library2.dart' as lib;
-
-const lazy = const DeferredLibrary('deferred_class_library2');
+import 'deferred_class_library2.dart' deferred as lib;
 
 main() {
   asyncStart();
-  lazy.load().then((_) {
+  lib.loadLibrary().then((_) {
     // Only Gee2.n888 to make sure no other constant pulls in its super.
     Expect.equals(888, new lib.Gee2.n888().value);
     asyncEnd();