Remove code supporting incremental compilation in dart2js

pkg/compiler/lib/src/js_backend/constant_handler_javascript.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 '../compile_time_constants.dart';
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
 import '../elements/elements.dart';
@@ skipping 216 matching lines @@
   }
 
   @override
   ConstantExpression compileMetadata(
       MetadataAnnotation metadata, Node node, TreeElements elements) {
     ConstantExpression constant =
         super.compileMetadata(metadata, node, elements);
     metadataConstantMap[metadata] = constant;
     return constant;
   }
-
-  void forgetElement(Element element) {
-    super.forgetElement(element);
-    const ForgetConstantElementVisitor().visit(element, this);
-    if (element is AstElement && element.hasNode) {
-      element.node.accept(new ForgetConstantNodeVisitor(this));
-    }
-  }
 }
 
 class ForgetConstantElementVisitor
     extends BaseElementVisitor<dynamic, JavaScriptConstantCompiler> {
   const ForgetConstantElementVisitor();
 
   void visitElement(Element e, JavaScriptConstantCompiler constants) {
     for (MetadataAnnotation data in e.implementation.metadata) {
       constants.metadataConstantMap.remove(data);
       if (data.hasNode) {
@@ skipping 14 matching lines @@
 class ForgetConstantNodeVisitor extends Visitor {
   final JavaScriptConstantCompiler constants;
 
   ForgetConstantNodeVisitor(this.constants);
 
   void visitNode(Node node) {
     node.visitChildren(this);
     constants.nodeConstantMap.remove(node);
   }
 }