remove 3.1 link

Doc/tools/sphinxext/indexsidebar.html

@@ -4,7 +4,6 @@
 	    <ul>
 	      <li><a href="http://docs.python.org/2.6/">Python 2.6 (stable)</a></li>
 	      <li><a href="http://docs.python.org/2.7/">Python 2.7 (in development)</a></li>
-	      <li><a href="http://docs.python.org/3.1/">Python 3.1 (stable)</a></li>
 	      <li><a href="http://docs.python.org/dev/py3k/">Python 3.2 (in development)</a></li>
               <li><a href="http://www.python.org/doc/versions/">Old versions</a></li>
             </ul>