[tz] Getting current tzdb version in use

[Paul Eggert]

Robert Elz wrote:
> Which we don't in NetBSD, that file adds no value for us.

The main intent of the tzdata.zi file was to have a single file containing all 
the information of all the TZif files, so that a software upgrade procedure 
could get a copy of tzdata.zi and then run zic to generate the other files. 
tzdata.zi is considerably smaller than a tarball of the TZif files it 
represents: a factor of 4 smaller if you use gzip to compress both, and a factor 
of 3 smaller even if you use lzip which is much better at compressing.

It'd be cool to update all the TZif data by downloading a tzdata.zi.lz file that 
contains only 21556 bytes (the current size). This particular bit of 
microoptimization hasn't caught on yet, but perhaps some day it will in IoT 
devices where those bytes still count.