Now that we've completed the k6 docs migration from k6.io/docs to grafana.com/docs/k6, we should be able to delete the old source files for the k6.io/docs website that live under https://github.com/grafana/k6-docs/tree/main/src.

• Test that deleting files won't impact redirects
  • Test PR deleting one file Delete legacy docs (one page test) #1810
  • Need to double-check after invalidating cache
• Check any GitHub Action workflows that need to be updated/removed
• Check any build files and other folders for files that can be removed