minor #17792 [Form] remove useless code in ResizeFormListener (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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[Form] remove useless code in ResizeFormListener

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
-------

088c20c [Form] remove useless code in ResizeFormListener

src/Symfony/Component/Form/Extension/Core/EventListener/ResizeFormListener.php

@@ -96,10 +96,6 @@ class ResizeFormListener implements EventSubscriberInterface
         $form = $event->getForm();
         $data = $event->getData();
 
-        if (null === $data || '' === $data) {
-            $data = array();
-        }
-
         if (!is_array($data) && !($data instanceof \Traversable && $data instanceof \ArrayAccess)) {
             $data = array();
         }