[docs] remove reference to symfony_bridges in TwigExtension docs

doc/extensions/twig.rst

@@ -21,11 +21,6 @@ Parameters
 * **twig.class_path** (optional): Path to where the Twig
   library is located.
 
-* **symfony_bridges** (optional): Set this to true if you want
-  to integrate the ``UrlGeneratorExtension`` and the
-  ``TranslationExtension`` with Twig. This requires loading
-  Symfony2 ``Bridge`` classes which include those Twig extensions.
-
 Services
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