Remove code supporting incremental compilation in dart2js

pkg/compiler/lib/src/serialization/modelz.dart

 // Copyright (c) 2015, 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.
 
 /// Implementation of the element model used for deserialiation.
 ///
 /// These classes are created by [ElementDeserializer] triggered by the
 /// [Deserializer].
 
 library dart2js.serialization.modelz;
@@ skipping 1553 matching lines @@
   final List<FunctionElement> nestedClosures = <FunctionElement>[];
 
   @override
   MemberElement get memberContext => this;
 
   @override
   Name get memberName => new Name(name, library);
 
   @override
   bool get isInjected => _decoder.getBool(Key.IS_INJECTED);
-
-  @override
-  void forgetElement() {
-    nestedClosures.clear();
-  }
 }
 
 abstract class FieldElementZ extends DeserializedElementZ
     with
         AnalyzableElementMixin,
         AstElementMixinZ,
         TypedElementMixin,
         MemberElementMixin
     implements FieldElement {
   bool _isConst;
@@ skipping 817 matching lines @@
   }
 
   @override
   Node get node => throw new UnsupportedError('${this}.node');
 
   @override
   bool get hasNode => false;
 
   String toString() => 'MetadataAnnotationZ(${constant.toDartText()})';
 }