dart2js: remove JS_OBJECT_CLASS_NAME and JS_NULL_CLASS_NAME from foreign

sdk/lib/_internal/compiler/js_lib/foreign_helper.dart

 // Copyright (c) 2012, 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.
 
 library _foreign_helper;
 
 import 'dart:_js_embedded_names' show JsGetName, JsBuiltin;
 
 /**
  * Emits a JavaScript code fragment parameterized by arguments.
@@ skipping 184 matching lines @@
  * an interface, e.g. `JS_INTERCEPTOR_CONSTANT(JSInt)`, not
  * `JS_INTERCEPTOR_CONSTANT(int)`.
  */
 JS_INTERCEPTOR_CONSTANT(Type type) {}
 
 /**
  * Returns the prefix used for generated type argument substitutions on classes.
  */
 String JS_OPERATOR_AS_PREFIX() {}
 
-/// Returns the name of the class `Object` in the generated code.
-String JS_OBJECT_CLASS_NAME() {}
-
-/// Returns the name of the class `Null` in the generated code.
-String JS_NULL_CLASS_NAME() {}
-
 /**
  * Returns the field name used for determining if an object or its
  * interceptor has JavaScript indexing behavior.
  */
 String JS_IS_INDEXABLE_FIELD_NAME() {}
 
 /**
  * Returns the object corresponding to Namer.CURRENT_ISOLATE.
  */
 JS_CURRENT_ISOLATE() {}
@@ skipping 87 matching lines @@
 }
 
 /**
  * JavaScript string concatenation. Inputs must be Strings.  Corresponds to the
  * HStringConcat SSA instruction and may be constant-folded.
  */
 String JS_STRING_CONCAT(String a, String b) {
   // This body is unused, only here for type analysis.
   return JS('String', '# + #', a, b);
 }