Revert datasets authentication with DownloadConfig
Once we update `datasets` to version 2.14.4, we no longer need the authentication tweaks (where we had to use `download_config` instead of `token`) introduced by:
- #1620

Fix #1659.
Revert datasets authentication with DownloadConfig: Once we update `datasets` to version 2.14.4, we no longer need the authentication tweaks (where we had to use `download_config` instead of `token`) introduced by:
- #1620

Fix #1659.