Feature Request Checklist

• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

As of #3038, --compilers is deprecated and non-functional. I've yet to see anybody use it in any real projects. But the code still exists:

This is dead weight on the project. IMO there's no real need to keep it around given how it's been deprecated with a loud warning & migration docs (https://github.com/mochajs/mocha/wiki/compilers-deprecation) for 7 years.

Suggested Solution

I propose we remove it in a future major version, such as Mocha 12.

Alternatives

We could leave it in, but all it does now is throw createUnsupportedError.

Additional Info

Similar sibling issue: #5243