Do not mention swiftmailer since it's unsupported

Problem/Motivation

at /admin/structure/contact/settings, in the description of the [ ] Send HTML checkbox we mention the deprecated Swiftmailer module → .

Proposed resolution

Please substitute it with what's already suggested in that module's page, ie. Drupal Symfony Mailer Lite → or Drupal Symfony Mailer → so that users don't waste time and think this module is deprecated as well.