Remove support for the DeferredLibrary annotation and remove tests of it

tests/compiler/dart2js/deferred_load_graph_segmentation_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.
 
 // Test of the graph segmentation algorithm used by deferred loading
 // to determine which elements can be deferred and which libraries
 // much be included in the initial download (loaded eagerly).
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 101 matching lines @@
 // Both lib1 and lib2 import lib3 directly and
 // both use lib3.foo3.  Therefore a shared output unit for lib1 and lib2 should
 // be created.
 //
 // lib1 and lib2 also import lib4 deferred, but lib1 uses lib4.bar1 and lib2
 // uses lib4.bar2.  So two output units should be created for lib4, one for each
 // import.
 const Map MEMORY_SOURCE_FILES = const {
   "main.dart":"""
 import "dart:async";
-@def_main_1 import 'lib1.dart' as l1;
-@def_main_2 import 'lib2.dart' as l2;
-
-const def_main_1 = const DeferredLibrary("lib1");
-const def_main_2 = const DeferredLibrary("lib2");
+import 'lib1.dart' deferred as lib1;
+import 'lib2.dart' deferred as lib2;
 
 void main() {
-  def_main_1.load().then((_) {
-        l1.foo1();
-        new l1.C();
-    def_main_2.load().then((_) {
-        l2.foo2();
+  lib1.loadLibrary().then((_) {
+        lib1.foo1();
+        new lib1.C();
+    lib2.loadLibrary().then((_) {
+        lib2.foo2();
     });
   });
 }
 """,
   "lib1.dart":"""
 library lib1;
 import "dart:async";
 import "dart:html";
 
 import "lib3.dart" as l3;
-@def_1_1 import "lib4.dart" as l4;
-
-const def_1_1 = const DeferredLibrary("lib4_1");
+import "lib4.dart" deferred as lib4_1;
 
 class C {}
 
 foo1() {
   new InputElement();
-  def_1_1.load().then((_) {
-    l4.bar1();
+  lib4_1.loadLibrary().then((_) {
+    lib4_1.bar1();
   });
   return () {return 1 + l3.foo3();} ();
 }
 """,
   "lib2.dart":"""
 library lib2;
 import "dart:async";
 import "lib3.dart" as l3;
-@def_2_1 import "lib4.dart" as l4;
-
-const def_2_1 = const DeferredLibrary("lib4_2");
+import "lib4.dart" deferred as lib4_2;
 
 foo2() {
-  def_2_1.load().then((_) {
-    l4.bar2();
+  lib4_2.loadLibrary().then((_) {
+    lib4_2.bar2();
   });
   return () {return 2+l3.foo3();} ();
 }
 """,
   "lib3.dart":"""
 library lib3;
 
 foo3() {
   return () {return 3;} ();
 }
 """,
   "lib4.dart":"""
 library lib4;
 
 bar1() {
   return "hello";
 }
 
 bar2() {
   return 2;
 }
 """,
 };