hwclock: Remove TZUTC

hwclock: Remove TZUTC

commit d53f8ecfbf036eddb2aef737dc0973a613d80ced
introduced the TZUTC environment variable to
facilitate use of the zoneinfo 'right' database.
This was incorrect. Either the TZDIR environment
variable should be used or a system-wide
configuration for the 'right' database should be
used.

See hwclock(8) POSIX vs 'RIGHT' for more details.

TZUTC was undocumented and should be safe to remove.

The commit also caused a regression when using
musl libc, because when TZUTC is unset getenv()
returns a NULL pointer.
Reported-by: Isaac Dunham <ibid.ag@gmail.com>
Signed-off-by: J William Piggott <elseifthen@gmx.com>