Remove backends.

compiler/java/com/google/dart/compiler/backend/js/ast/JsValueLiteral.java

-// Copyright (c) 2011, 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.
-
-package com.google.dart.compiler.backend.js.ast;
-
-/**
- * A JavaScript string literal expression.
- */
-public abstract class JsValueLiteral extends JsLiteral {
-
-  protected JsValueLiteral() {
-  }
-
-  @Override
-  public final boolean hasSideEffects() {
-    return false;
-  }
-
-  @Override
-  public final boolean isLeaf() {
-    return true;
-  }
-}