Remove rhino - it's no longer used anywhere.

compiler/build.xml

 <!--
   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.
  -->
 <project default="dist">
   <!--
       EDIT DARTC.XML FIRST.  This file is no longer used to build
       dartc proper.  It is only here to avoid breaking dartium.gyp
       short term.  Change dartc.xml to get everything working, 
@@ skipping 29 matching lines @@
 
   <property name="test_py" location="../tools/test.py"/>
 
   <!--
     Define buildtime and runtime classpaths.
   -->
   <path id="classpath.compile">
     <pathelement location="${third_party.dir}/args4j/2.0.12/args4j-2.0.12.jar"/>
     <pathelement location="${third_party.dir}/guava/r09/guava-r09.jar"/>
     <pathelement location="${third_party.dir}/json/r2_20080312/json.jar"/>
-    <pathelement location="${third_party.dir}/rhino/1_7R3/js.jar"/>
   </path>
 
   <path id="classpath.runtime">
     <path refid="classpath.compile"/>
   </path>
 
   <path id="classpath.compile.tests">
     <path refid="classpath.compile"/>
     <pathelement location="${build.classes.dir}"/>
     <pathelement location="${third_party.dir}/junit/v4_8_2/junit.jar"/>
@@ skipping 117 matching lines @@
 
   <target name="clean" description="Deletes the build output directory.">
     <delete dir="${build.dir}"/>
     <delete dir="${dist.dir}"/>
   </target>
 
   <target name="tests.jar" depends="compile-tests">
     <jar destfile="${build.dir}/tests.jar" basedir="${build.test.classes.dir}"/>
   </target>
 </project>