[3.12] gh-111276: Clarify docs and comments about the role of LC_CTYPE (GH-111319) (#111391)

Fix locale.LC_CTYPE documentation to no longer mention string.lower() et al. Those functions were removed in Python 3.0:
https://docs.python.org/2/library/string.htmlGH-deprecated-string-functions

Also, fix a comment in logging about locale-specific behavior of `str.lower()`.

(cherry picked from commit 6d42759c5e47ab62d60a72b4ff15d29864554579)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>