CLN: Remove unused functions
It's pretty hard to be 100% sure that these non-private functions are unused, but I'm pretty sure that they are not commonly used, if at all, after some searches in Google, GitHub, and pandas doc.
Keep them coming! @tqa236  @mroeschke thanks! I'm combing through `vulture` to see what can be removed. May I know where the documentation about the private directories is, please? It'll surely help me decide if a report is a true or false positive > May I know where the documentation about the private directories is, please?

https://pandas.pydata.org/docs/reference/index.html#api-reference Thank you!