Remove code supporting incremental compilation in dart2js

pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart

Index: pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
diff --git a/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart b/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
index 4847928a9ee44209347293b8f112850fdbb8d1d2..479ab20c95b4a2579fd022866c47759dd516d7d9 100644
--- a/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
+++ b/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
@@ -234,14 +234,6 @@ class JavaScriptConstantCompiler extends ConstantCompilerBase
     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