Remove unused documentation branches

[arisp99]

Maintenance Request

Now that we have ported over the documentation for this project to Read the Docs, we should clean up this project by removing outdated branches.

We can likely remove:

• [x] The prodution-docs branch which was used for storing the source code for the production documentation. At this point in time, this was v0.4.0.
• [x] The prod-gh-pages GitHub page branch which was the associated GitHub pages branch with the production docs.
• [x] The master gh-pages branch which had the GitHub pages information for the master branch.
• [x] Workflows for building the docs for GitHub pages.