Remove support for the DeferredLibrary annotation and remove tests of it

tests/compiler/dart2js_extra/deferred/deferred_constant_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 
 import 'dart:async';
 
-@lazy import 'deferred_class_library.dart';
-
-const lazy = const DeferredLibrary('deferred_class_library');
+import 'deferred_class_library.dart' deferred as lib;
 
 main() {
   var x;
-  Expect.throws(() => const MyClass());
-  Expect.throws(() => const Constant(42));
-  Expect.throws(() => const [const Constant(42)]);
+  Expect.throws(() => const lib.MyClass());
+  Expect.throws(() => const lib.Constant(42));
+  Expect.throws(() => const [const lib.Constant(42)]);
   int counter = 0;
   asyncStart();
-  lazy.load().then((bool didLoad) {
-    Expect.isTrue(didLoad);
+  lib.loadLibrary().then((_) {
     Expect.equals(1, ++counter);
-    print('deferred_class_library was loaded');
-    x = const MyClass();
+    x = const lib.MyClass();
     Expect.equals(42, x.foo(87));
-    Expect.listEquals(const [const Constant(42)], [new Constant(42)]);
+    Expect.listEquals(const [const lib.Constant(42)], [new lib.Constant(42)]);
     asyncEnd();
   });
   Expect.equals(0, counter);
   Expect.isNull(x);
   asyncStart();
-  lazy.load().then((bool didLoad) {
+  lazy.load().then((_) {
     Expect.isFalse(didLoad);
     Expect.equals(2, ++counter);
-    print('deferred_class_library was loaded');
-    x = const MyClass();
+    x = const lib.MyClass();
     Expect.equals(42, x.foo(87));
-    Expect.listEquals(const [const Constant(42)], [new Constant(42)]);
+    Expect.listEquals(const [const lib.Constant(42)], [new lib.Constant(42)]);
     asyncEnd();
   });
   Expect.equals(0, counter);
   Expect.isNull(x);
-  Expect.throws(() => const Constant(42));
-  Expect.throws(() => const [const Constant(42)]);
+  Expect.throws(() => const lib.Constant(42));
+  Expect.throws(() => const [const lib.Constant(42)]);
   Expect.isNull(x);
 }