minor symfony#17838 Remove duplicate validation in RedirectResponse (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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Remove duplicate validation in RedirectResponse

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

Commits
-------

d27c4f4 Remove duplicate validation in RedirectResponse

Author: fabpot

src/Symfony/Component/HttpFoundation/RedirectResponse.php

@@ -33,10 +33,6 @@ class RedirectResponse extends Response
      */
     public function __construct($url, $status = 302, $headers = array())
     {
-        if (empty($url)) {
-            throw new \InvalidArgumentException('Cannot redirect to an empty URL.');
-        }
-
         parent::__construct('', $status, $headers);
 
         $this->setTargetUrl($url);