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');
-
-main() {
-  var x;
-  Expect.throws(() => const MyClass());
-  Expect.throws(() => const Constant(42));
-  Expect.throws(() => const [const Constant(42)]);
-  int counter = 0;
-  asyncStart();
-  lazy.load().then((bool didLoad) {
-    Expect.isTrue(didLoad);
-    Expect.equals(1, ++counter);
-    print('deferred_class_library was loaded');
-    x = const MyClass();
-    Expect.equals(42, x.foo(87));
-    Expect.listEquals(const [const Constant(42)], [new Constant(42)]);
-    asyncEnd();
-  });
-  Expect.equals(0, counter);
-  Expect.isNull(x);
-  asyncStart();
-  lazy.load().then((bool didLoad) {
-    Expect.isFalse(didLoad);
-    Expect.equals(2, ++counter);
-    print('deferred_class_library was loaded');
-    x = const MyClass();
-    Expect.equals(42, x.foo(87));
-    Expect.listEquals(const [const Constant(42)], [new Constant(42)]);
-    asyncEnd();
-  });
-  Expect.equals(0, counter);
-  Expect.isNull(x);
-  Expect.throws(() => const Constant(42));
-  Expect.throws(() => const [const Constant(42)]);
-  Expect.isNull(x);
-}