minor #6862 Remove unused JsonResponse dependency in example (Farskies)

This PR was submitted for the 3.1 branch but it was merged into the 2.7 branch instead (closes #6862).

Discussion
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Remove unused JsonResponse dependency in example

Commits
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60d5164 Remove unused JsonResponse dependency in example

controller.rst

@@ -498,7 +498,6 @@ abstraction around the HTTP response - the text-based message filled with
 headers and content that's sent back to the client::
 
     use Symfony\Component\HttpFoundation\Response;
-    use Symfony\Component\HttpFoundation\JsonResponse;
 
     // create a simple Response with a 200 status code (the default)
     $response = new Response('Hello '.$name, Response::HTTP_OK);