Don't use binderbot!

[brian-rose]

This PR tests the new switch to disable executing via binderbot.

I don't think this should be merged, rather I think the default in the template should use binderbot, as in #90. But we want to test this option (and document its use).

[github-actions]

👋 Thanks for opening this PR! The Cookbook will be automatically built with GitHub Actions. To see the status of your deployment, click below.
🔍 Git commit SHA: 533d4b6
✅ Deployment Preview URL: https://ProjectPythiaCookbooks.github.io/cookbook-template/_preview/91

[brian-rose]

Differences include:

• there is no separate book-build-environment.yml (not needed)
• all dependencies including jupyter book and the sphinx theme need to be in environment.yml
• _config.yml must declare the execute_notebooks option appropriately
• Each call to the build-book.yaml workflow must declare inputs including environment_name, environment_file, and use_binder (rather than using default values, because the defaults assume that use_binder is true)

[brian-rose]

Both this and #90 are working now.

But if we're going to have a switch to toggle Binder execution on and off, it should be simpler (i.e. fewer edits needed in the repo).

Maybe a better approach is to get rid of the book-build-environment.yml file and associated defaults in ProjectPythia/cookbook-actions#19 in favor of a single environment.yml. We can "hard code" the minimal book build environment in the workflow files for the case where we're executing via binder.