minor #9029 [error_pages] Removing misleading is_granted checker in code example (Marek Szymeczko)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #9029).

Discussion
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[error_pages] Removing misleading `is_granted` checker in code example

Docs contain misleading code section that leaves you wondering for a while ;)

This commit clearly states that it's no longer possible:
https://github.com/symfony/symfony/pull/5325/files

Commits
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64a996b [error_pages] Removing misleading  checker in code example

Author: javiereguiluz

controller/error_pages.rst

@@ -99,11 +99,6 @@ To override the 404 error template for HTML pages, create a new
     {% block body %}
         <h1>Page not found</h1>
 
-        {# example security usage, see below #}
-        {% if app.user and is_granted('IS_AUTHENTICATED_FULLY') %}
-            {# ... #}
-        {% endif %}
-
         <p>
             The requested page couldn't be located. Checkout for any URL
             misspelling or <a href="{{ path('homepage') }}">return to the homepage</a>.