removed obsolete documentation about requiring classes

doc/advanced.rst

@@ -645,9 +645,6 @@ main ``Environment`` object::
     $twig = new Twig_Environment($loader);
     $twig->addExtension(new Project_Twig_Extension());
 
-Of course, you need to first load the extension file by either using
-``require_once()`` or by using an autoloader (see `spl_autoload_register()`_).
-
 .. tip::
 
     The bundled extensions are great examples of how extensions work.
@@ -866,7 +863,6 @@ Testing the node visitors can be complex, so extend your test cases from
 ``Twig_Test_NodeTestCase``. Examples can be found in the Twig repository
 `tests/Twig/Node`_ directory.
 
-.. _`spl_autoload_register()`: http://www.php.net/spl_autoload_register
 .. _`rot13`:                   http://www.php.net/manual/en/function.str-rot13.php
 .. _`tests/Twig/Fixtures`:     https://github.com/twigphp/Twig/tree/master/test/Twig/Tests/Fixtures
 .. _`tests/Twig/Node`:         https://github.com/twigphp/Twig/tree/master/test/Twig/Tests/Node