Remove daily_submission_emails_enabled feature flag

[SamJamCul]

What problem does this pull request solve?

https://trello.com/c/gPUPB7OH/2870-remove-feature-flags-for-daily-csvs-and-csv-add-another-answer-single-column

Things to consider when reviewing

• Ensure that you consider the wider context.
• Does it work when run on your machine?
• Is it clear what the code is doing?
• Do the commit messages explain why the changes were made?
• Are there all the unit tests needed?
• Do the end to end tests need updating before these changes will pass?
• Has all relevant documentation been updated?

[github-actions]

🎉 A review copy of this PR has been deployed! You can reach it at: https://pr-2623.admin.review.forms.service.gov.uk/

It may take 5 minutes or so for the application to be fully deployed and working. If it still isn't ready
after 5 minutes, there may be something wrong with the ECS task. You will need to go to the integration AWS account
to debug, or otherwise ask an infrastructure person.

For the sign in details and more information, see the review apps wiki page.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud