Fix doc build CI job

Author: oscarbenjamin

.github/workflows/buildwheel.yml

@@ -134,7 +134,6 @@ jobs:
 
       - run: pip install --upgrade pip
       - run: pip install -r requirements-dev.txt
-      - run: pip install --no-index --find-links wheelhouse python_flint
       - run: pytest --doctest-glob='*.rst' doc/source
       - run: spin docs