minor symfony#19757 Remove the warning marking the symfony server config file as experimental (stof)

This PR was merged into the 5.4 branch.

Discussion
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Remove the warning marking the symfony server config file as experimental

I validated with Fabien that this is not experimental anymore.

Commits
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7dd0472 Remove the warning marking the symfony server config file as experimental

Author: javiereguiluz

setup/symfony_server.rst

@@ -307,11 +307,6 @@ server provides a ``run`` command to wrap them as follows:
 Configuration file
 ------------------
 
-.. caution::
-
-    This feature is experimental and could change or be removed at any time
-    without prior notice.
-
 There are several options that you can set using a ``.symfony.local.yaml`` config file:
 
 .. code-block:: yaml