Fix documentation

[bonjourmauko]

Depended upon by openfisca/openfisca-doc#283

Bug fix

• Fix documentation
  • Suppression of some modules broke the documentation build

[benjello]

@maukoquiroga : just to let you know that these changes broke the baremes-ipp generation page and that we fixed it by using python3.9 and importing importlib-metadata. You may consider adding this dep.

Do not know if it is an issue or another problem.

[MattiSG]

If a patch bump forces changing the Python version, this is a big problem and that new version should be yanked asap.

[benjello]

The major problem was importlib_metadata. I bumped the python version to anticipate future deprecations.