Remove CDN and benchmark workflows (#7001)

# Pull Request

## 📖 Description

The following GitHub workflows have been removed:
- CDN workflow - we are now using GitHub pages, as such we no longer need to deploy to Azure.
- Benchmarking workflow - we are no longer using the same benchmarking utility as the package has been removed, there will be some additional work later to benchmark packages and produce results for PRs in future, but that will be added to the validate PR workflow.

## ✅ Checklist

### General

<!--- Review the list and put an x in the boxes that apply. -->

- [ ] I have included a change request file using `$ npm run change`
- [ ] I have added tests for my changes.
- [x] I have tested my changes.
- [ ] I have updated the project documentation to reflect my changes.
- [x] I have read the [CONTRIBUTING](https://github.com/microsoft/fast/blob/master/CONTRIBUTING.md) documentation and followed the [standards](https://github.com/microsoft/fast/blob/master/CODE_OF_CONDUCT.md#our-standards) for this project.