Doc make.py clean

[TomAugspurger]

@jorisvandenbossche @datapythonista currently _sphinx_build in doc/make.py always calls clean. Do you know why that was added?

My doc-build process in https://github.com/pandas-dev/pandas-release assumes that I can do make.py html and make.py latex_forced.

An option to not clean would be fine by me.

[jorisvandenbossche]

It seems to have been added recently in #24428

@datapythonista was there a technical reason for that PR (for the faster building of single pages) that it was needed?

I would personally prefer to not always clean by default, but an option is fine as well.

[datapythonista]

Sorry about that. Yes, I added it. It's not required, but I thought it made more sense to just leave the files that were built in the last run, mainly for the single pages. I had some cases where I wasn't sure what was built and what was already there. But it's perfectly fine to remove it, and call make.py clean explicitly, I just didn't think it would be a problem for anyone.