Update services.xml

Fixes:
```
  [Symfony\Component\DependencyInjection\Exception\InvalidArgumentException]
  Unable to replace alias "swiftmailer.mailer.default.spool.automailer" with "swiftmailer.mailer.default.spool".

  [Symfony\Component\DependencyInjection\Exception\InvalidArgumentException]
  The service definition "swiftmailer.mailer.default.spool.automailer" does not exist.
```