minor #34176 [4.3] Remove unused local variables (fancyweb)

This PR was merged into the 4.3 branch.

Discussion
----------

[4.3] Remove unused local variables

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Follow up of symfony/symfony#34105 on 4.3.

Commits
-------

58161b8eec [4.3] Remove unused local variables

Author: nicolas-grekas

Response/ResponseTrait.php

@@ -104,7 +104,6 @@ public function getContent(bool $throw = true): string
 
         if (null === $this->content) {
             $content = null;
-            $chunk = null;
 
             foreach (self::stream([$this]) as $chunk) {
                 if (!$chunk->isLast()) {