* Rename unsubscribe to remove_from_mailchimp_newsletters
* Permanently delete from mailchimp instead of unsubscribing
* Rename method and remove comment
* Don't use i18n because of error message
We don't want to use i18n here because e.title comes from the error response. If a Forem
was using a different locale and Mailchimp for newsletters, they would still receive the
error response in English (because of Mailchimp).
* Refactor and rename a bit
* Rename methods in tests accordingly
* Remove now moot test
* Rename method in other places it was previously called
* Remove unused translation, see 62fee247ee2565e4d3d14919a8636a76ce5ecc9f
* Fix typo and report error if not 404
0fca6a6f35