Remove retired and security branches from active docs (#3879)

Doc/tools/static/switchers.js

@@ -12,9 +12,6 @@
   var all_versions = {
     '3.7': 'dev (3.7)',
     '3.6': '3.6',
-    '3.5': '3.5',
-    '3.4': '3.4',
-    '3.3': '3.3',
     '2.7': '2.7',
   };
 

Doc/tools/templates/indexsidebar.html

@@ -3,7 +3,6 @@
 <h3>{% trans %}Docs for other versions{% endtrans %}</h3>
 <ul>
   <li><a href="https://docs.python.org/2.7/">{% trans %}Python 2.7 (stable){% endtrans %}</a></li>
-  <li><a href="https://docs.python.org/3.5/">{% trans %}Python 3.5 (stable){% endtrans %}</a></li>
   <li><a href="https://docs.python.org/3.6/">{% trans %}Python 3.6 (stable){% endtrans %}</a></li>
   <li><a href="https://www.python.org/doc/versions/">{% trans %}Old versions{% endtrans %}</a></li>
 </ul>