bpo-34544: Fix setlocale() in pymain_read_conf() (GH-9041)

bpo-34485, bpo-34544: On some FreeBSD, nl_langinfo(CODESET) fails if
LC_ALL or LC_CTYPE is set to an invalid locale name. Replace
_Py_SetLocaleFromEnv(LC_CTYPE) with _Py_SetLocaleFromEnv(LC_ALL) to
initialize properly locales.

Partially revert commit 177d921c8c03d30daa32994362023f777624b10d.