Remove unused API.

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

Index: dart/sdk/lib/_internal/compiler/implementation/js/builder.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/js/builder.dart b/dart/sdk/lib/_internal/compiler/implementation/js/builder.dart
index e02bd0087c6cd5c0083a4248e53e632bccb59482..8958b50fcc2f3b6cc5a191684b8fd5b5764d60d4 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/js/builder.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/js/builder.dart
@@ -90,12 +90,6 @@ class JsBuilder {
     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);