minor #20120 [Security] Remove note about stateless firewalls marking routes as stateless (MatTheCat)

This PR was merged into the 6.4 branch.

Discussion
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[Security] Remove note about stateless firewalls marking routes as stateless

Following symfony/symfony#58017

Commits
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768ef5a [Security] Remove note about stateless firewalls marking routes as stateless

Author: javiereguiluz

reference/configuration/security.rst

@@ -1075,13 +1075,6 @@ the session must not be used when authenticating users:
             // ...
         };
 
-Routes under this firewall will be :ref:`configured stateless <stateless-routing>`
-when they are not explicitly configured stateless or not.
-
-.. versionadded:: 6.3
-
-    Stateless firewall marking routes stateless was introduced in Symfony 6.3.
-
 User Checkers
 ~~~~~~~~~~~~~