Remove Docusaurus leftovers

[aldur]

Describe the issue The repository source still includes some assets specific to Docusaurus (e.g. docusaurus.config.js). This can make it confusing to newcomers who make contributions and would like to check their work locally before submitting a PR (just happened to me).

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[eric-stacks]

docs repo no longer consists of docusaurus leftovers, closing issue for now.