As QT5 will be deprecated soon, drop the QT5 flavor.

Reviewed by:		kde (arrowd)
Differential Revision:	https://reviews.freebsd.org/D58170

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

and strip all lower bounds of 3.9 or 3.10 because they are implied now.

python:3.9-X  -> python:-X
python:3.9+   -> python
python:3.10-X -> python:-X
python:3.10+  -> python
(options such as ,build preserved)