Removing "CMOS clock set to UTC" question

Our installer asks (via tzsetup):

> Is this machine's CMOS clock set to UTC?  If it is set to local time,
> or you don't know, please choose NO here!

I've heard many reports of new users being confused by this question
when installing FreeBSD for the first time. I don't think it provides
much value; it is a minor convenience for dual-booting with Windows
but imposes a cost on everyone installing FreeBSD. It is trivial to
configure the system to use local time in the system's real-time clock
by creating /etc/wall_cmos_clock. Other operating systems do not ask,
they just default to local time (Windows) or UTC (everyone else).

I've proposed removing the question from bsdinstall in
https://reviews.freebsd.org/D45569.