Remove unused API.

dart/sdk/lib/_internal/compiler/implementation/js/builder.dart

 // Copyright (c) 2013, 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.
 
 // Utilities for building JS ASTs at runtime.  Contains a builder class
 // and a parser that parses part of the language.
 
 part of js;
 
 class JsBuilder {
@@ skipping 72 matching lines @@
       } else {
         throw new ArgumentError('parameter should be a String or a Parameter');
       }
     }
     if (parameters is! List) {
       parameters = [parameters];
     }
     return new Fun(parameters.map(toParameter).toList(), block(body));
   }
 
-  Assignment assign(Expression leftHandSide, Expression value) {
-    return new Assignment(leftHandSide, value);
-  }
-
-  Expression undefined() => new Prefix('void', new LiteralNumber('0'));
-
   VariableDeclarationList defineVar(String name, [initializer]) {
     if (initializer != null) {
       initializer = toExpression(initializer);
     }
     var declaration = new VariableDeclaration(name);
     var initialization = [new VariableInitialization(declaration, initializer)];
     return new VariableDeclarationList(initialization);
   }
 
   Statement toStatement(statement) {
@@ skipping 689 matching lines @@
   }
 
   Node visitLiteralNull(LiteralNull node) {
     return node;
   }
 
   Node visitLiteralBool(LiteralBool node) {
     return node;
   }
 }