CLN: Remove unused script find_commits_touching_func.py
- [X] xref #31039

I've been trying the script `find_commits_touching_func.py` and doesn't seem to be working. Tried for many existing functions, and never get any result. I guess it doesn't work with newer git versions, or with the latest dependencies. And if nobody realized of this before, I assume nobody is using this script (and in any case, a separate project would be more appropriate for it, since I don't think it's pandas specific).

The script was being refactored in #32044, that's why I was having a look.
