bsdinstall: skip tzsetup UTC question

During installation bsdinstall 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!

Most operating systems, except for Windows, use UTC in the hardware
real-time clock by default. This question from tzsetup is presumably
intended to aid in dual-boot-with-Windows configurations, but these
represent a fraction of all FreeBSD installs.

Rather than asking this question on every install just default to UTC.
Users who want to dual-boot Windows can create /etc/wall_cmos_clock.
We can look at making this smarter in the future.

Reviewed by: bapt, brooks, brd, cy, 0mp, ngie
Relnotes: yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D45569