fixup! Remove logo_only from docs config (no longer supported)

sphinx-book-theme 1.x apparently has an undocumented breaking change in
executablebooks/sphinx-book-theme#668 -- `logo_only`
is no longer supported, and instead there is a `logo` option that I haven't
looked into. I'm not sure what we want, but I'd rather unbreak and move on
so that we at least don't have a broken docs build.

python-template/{{cookiecutter.placeholder_repo_name}}/docs/conf.py

@@ -195,7 +195,6 @@ def get_version(*file_paths):
     "repository_url": "https://github.com/{{ cookiecutter.github_org }}/{{ cookiecutter.repo_name }}",
     "repository_branch": 'main',
     "path_to_docs": "docs/",
-    "logo_only": True,
     "home_page_in_toc": True,
     "use_repository_button": True,
     "use_issues_button": True,