gh-111276: Clarify docs and comments about the role of LC_CTYPE (#111319)

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.html#deprecated-string-functions

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

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>