Revert "Create CSA region-to-email mapping YAML file for cyhy-mailer"

[dav3r]

🗣 Description

This PR reverts commit 1ca6c51, which was the primary commit in this PR:

• Create CSA region-to-email mapping YAML file for cisagov/cyhy-mailer #749

💭 Motivation and context

This was requested in cisagov/cyhy-system#129, please refer to that issue for more information.

🧪 Testing

Visual inspection.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.

✅ Post-merge checklist

• After Revert "Add secret and CLI option for CSA emails to Docker compositions" cyhy-mailer#117 has been deployed, manually delete /var/cyhy/cyhy-mailer/secrets/csa_emails.yml from the Production reporter instance (or redeploy the entire reporter instance, but that seems like overkill here).

[felddy]

Looks good... better late than never?