reverted "[Form] fixed default CSRF token generation as a token must be tied to the user somewhat"

This reverts commit d326c398e2721c996d9f45108c1ab0cdfceb8ea6.

src/Symfony/Component/Form/Form.php

@@ -60,7 +60,7 @@ class Form extends FieldGroup
         if (self::$defaultCsrfSecret !== null) {
             $this->setCsrfSecret(self::$defaultCsrfSecret);
         } else {
-            $this->setCsrfSecret(md5(__FILE__.session_id()));
+            $this->setCsrfSecret(md5(__FILE__.php_uname()));
         }
 
         if (self::$defaultCsrfProtection !== false) {