*/*: Use C.UTF-8 locale

Ports 02f27a83b44d fixed the ports tree to the C locale so it would work
correctly in environments where users use a locale that isn't compatible
with the C locale, e.g. xx_YY.UTF-8 where [A-Z] includes more than just
upper case letters. USE_LOCALE was introduced to let ports use another
locale if they needed it. The C.UTF-8 locale was created later on to be
mostly compatible with the C locale.

Switch the ports tree locale to C.UTF-8 and remove USE_LOCALE. The
world has moved to Unicode so all ports either require it or know how to
build correctly in a Unicode environment.

PR: 295945
Exp-run by: antoine