DOCS: Refactor nb/census income xgboost

[CloseChoice]

Overview

Works towards #3036

Description of the changes proposed in this pull request:

• clean up Census XGBoost notebook. There was not much to do, just remove some unnecessary commands and one typo

Checklist

• All pre-commit checks pass.

[connortann]

Thanks for the PR! A few comments from an initial look:

1. It looks like there are several warnings in the new rendered notebook, which should be addressed. I think these are related to 3rd party libraries like pandas- downgrading to pandas 1.x may help.
2. On a minor style note, may I suggest keeping the cell execution numbers? I think it looks visually nicer, and confirms to us maintainers that the notebook was run sequentially top-to-bottom in one run.

[CloseChoice]

Thanks for the review. I updated the notebook and fixed most of the warnings. There is still the "invalid value encountered in divide" error, but I cannot fix this with downgrading pandas.

[connortann]

Looks great, thanks for the PR!