Don't send rejection mails for all auto-generated mails

What does this MR do?

Don't send rejection mails for all auto-generated mails

Are there points in the code the reviewer needs to double check?

We don't need to include EmailHelpers. I'll make another merge request to fix other occurrences.

Why was this MR needed?

Try to fight over with https://gitlab.com/gitlab-org/gitlab-ce/issues/28472

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests
  • Added for this feature/bug
• Review
  • Has been reviewed by Backend

What are the relevant issue numbers?

Closes #28472 (closed)