Cannot apply sphinx-book-theme upgrade to cookiecutters (logo_only)

[timmc-edx]

Acceptance criteria:

• Ensure that cookiecutters docs config matches our official guide for docs (one way or another)

In #355 we discovered that the "logo_only": True present in the python-template's docs/conf.py was causing doc builds to fail. Specifically, using cookiecutter-python-library and then running make docs in the output results in the following error:

Warning, treated as error:
unsupported theme option 'logo_only' given

This is contrary to https://docs.openedx.org/en/latest/developers/how-tos/switch-to-the-sphinx-book-theme.html which gives a configuration that includes the setting. It's possible that the how-to is incorrect, or that it was correct at the time but sphinx-book-theme (now at 1.0.1) no longer supports it. In fact, only 4 repos seem to use this option, and 3 of them are on pre 1.0 versions of the theme.

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Update: See openedx/docs.openedx.org#345 in which there are changes to the guide, including removal of logo_only.