minor #11441 Update kernel.rst (atailouloute)

This PR was merged into the 3.4 branch.

Discussion
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Update kernel.rst

No need for the use statement

Commits
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acbec39 Update kernel.rst

Author: javiereguiluz

reference/configuration/kernel.rst

@@ -201,7 +201,6 @@ achieve a strict reproducible build:
     .. code-block:: php
 
         // app/config/services.php
-        use Symfony\Component\DependencyInjection\Reference;
 
         // ...
         $container->setParameter('kernel.container_build_time', '1234567890');