Remove support for the DeferredLibrary annotation and remove tests of it

tests/language/deferred_constraints_constants_old_syntax_test.dart

-// Copyright (c) 2014, 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 "dart:async";
-import 'package:expect/expect.dart';
-import 'package:async_helper/async_helper.dart';
-
-@lazy import "deferred_constraints_constants_old_syntax_lib.dart" as lib;
-
-const lazy = const DeferredLibrary('lib');
-
-const myConst1 =
-  lib.constantInstance; /// reference1: compile-time error
-  /*                    /// reference1: continued
-  499;
-  */                    /// reference1: continued
-const myConst2 =
-  lib.Const.instance; /// reference2: compile-time error
-  /*                  /// reference2: continued
-  499;
-  */                  /// reference2: continued
-
-void f1({a:
-  const lib.Const() /// default_argument1: compile-time error
-  /*                   /// default_argument1: continued
-  499
-  */                   /// default_argument1: continued
-}) {}
-
-void f2({a:
-  lib.constantInstance /// default_argument2: compile-time error
-  /*                         /// default_argument2: continued
-  499
-  */                         /// default_argument2: continued
-}) {}
-
-@lib.Const() /// metadata1: compile-time error
-class H1 {}
-@lib.Const.instance /// metadata2: compile-time error
-class H2 {}
-@lib.Const.namedConstructor() /// metadata3: compile-time error
-class H3 {}
-
-void main() {
-  var a1 = myConst1;
-  var a2 = myConst2;
-
-  asyncStart();
-  lazy.load().then((_) {
-    var instance = lib.constantInstance;
-    var c1 = const lib.Const(); /// constructor1: compile-time error
-    var c2 = const lib.Const.namedConstructor(); /// constructor2: compile-time error
-    f1();
-    f2();
-    var constInstance = lib.constantInstance; /// reference_after_load: ok
-    var h1 = new H1();
-    var h2 = new H2();
-    var h3 = new H3();
-    asyncEnd();
-  });
-}
-