remove unused reference

reference/configuration/framework.rst

@@ -1571,7 +1571,6 @@ Full Default Configuration
                 file_cache_dir:       '%kernel.cache_dir%/annotations'
                 debug:                '%kernel.debug%'
 
-.. _`protocol-relative`: http://tools.ietf.org/html/rfc3986#section-4.2
 .. _`HTTP Host header attacks`: http://www.skeletonscribe.net/2013/05/practical-http-host-header-attacks.html
 .. _`Security Advisory Blog post`: https://symfony.com/blog/security-releases-symfony-2-0-24-2-1-12-2-2-5-and-2-3-3-released#cve-2013-4752-request-gethost-poisoning
 .. _`Doctrine Cache`: http://docs.doctrine-project.org/projects/doctrine-common/en/latest/reference/caching.html