Update cache.rst

Remove unnecessary attributes

Co-authored-by: Nicolas Grekas <nicolas.grekas@gmail.com>

Author: mboelsterli

cache.rst

@@ -889,12 +889,8 @@ First, create a service that will compute the item's value::
     namespace App\Cache;
 
     use Psr\Cache\CacheItemInterface;
-    use Symfony\Component\DependencyInjection\Attribute\Autoconfigure;
-    use Symfony\Component\DependencyInjection\Attribute\AutoconfigureTag;
     use Symfony\Contracts\Cache\CallbackInterface;
 
-    #[Autoconfigure(tags: ['container.reversible'], public: true)]
-    #[AutoconfigureTag]
     class CacheComputation implements CallbackInterface
     {
         public function __invoke(CacheItemInterface $item, bool &$save): string