minor #20954 [Security] [Best practices] Remove mention of anonymous (MaximePinot)

This PR was merged into the 6.4 branch.

Discussion
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[Security] [Best practices] Remove mention of `anonymous`

As far as I know, the `anonymous` key does not exist any more.

Commits
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51200b2 [Security] [Best practices] Remove mention of `anonymous`

Author: javiereguiluz

best_practices.rst

@@ -362,10 +362,6 @@ Unless you have two legitimately different authentication systems and users
 (e.g. form login for the main site and a token system for your API only), it's
 recommended to have only one firewall to keep things simple.
 
-Additionally, you should use the ``anonymous`` key under your firewall. If you
-require users to be logged in for different sections of your site, use the
-:doc:`access_control </security/access_control>` option.
-
 Use the ``auto`` Password Hasher
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