Deprecate this module and mark it obsolete

See https://docs.drupalcommerce.org/commerce2/user-guide/checkout/allow-regi... last step!

That's super correct.
We have this feature in Core commerce itself.
Thanks for pointing that out.

A message should be clearly exposed in this project page.

Being this a time safer, I'm changing priority to major,

Thanks. Deprecation can be done like here:
https://www.drupal.org/project/filename_transliteration →

Added the Depreciation details for the Commerce Guest Logout module.