Remove support for the DeferredLibrary annotation and remove tests of it

sdk/lib/_internal/lib/async_patch.dart

Index: sdk/lib/_internal/lib/async_patch.dart
diff --git a/sdk/lib/_internal/lib/async_patch.dart b/sdk/lib/_internal/lib/async_patch.dart
index 004f433b54f36d8ebc6bc1758b8b371c9583a3e6..88ab1d0479a5dbbf8f3f721c8f460868ec73f943 100644
--- a/sdk/lib/_internal/lib/async_patch.dart
+++ b/sdk/lib/_internal/lib/async_patch.dart
@@ -8,7 +8,6 @@ import 'dart:_js_helper' show
     patch,
     Primitives,
     convertDartClosureToJS,
-    loadDeferredLibrary,
     requiresPreamble;
 import 'dart:_isolate_helper' show
     IsolateNatives,
@@ -91,7 +90,8 @@ class _AsyncRun {
 class DeferredLibrary {
   @patch
   Future<Null> load() {
-    return loadDeferredLibrary(libraryName, uri);
+    throw 'DeferredLibrary not supported. '
+          'please use the `import "lib.dart" deferred as lib` syntax.';
   }
 }