Removing "auto-generated" info

Reason: This creates the impression that this file should not be modified by the user. Whereas at https://symfony.com/doc/current/frontend/asset_mapper.html#page-specific-css-javascript there are instructions to modify this file.

symfony/asset-mapper/6.4/importmap.php

@@ -10,8 +10,6 @@
  *     be used as an "entrypoint" (and passed to the importmap() Twig function).
  *
  * The "importmap:require" command can be used to add new entries to this file.
- *
- * This file has been auto-generated by the importmap commands.
  */
 return [
     'app' => [