[tz] Removing systemv, pacificnew, Rule TYPEs, zic -y

[Tim Parenti]

I noticed recently that the systemv file, which adapted a subset of North
American zones with limited rulesets to old versions of System V, has had
all its once-useful bits commented out since 2005p.  Looking back at list
archives, even discussion at the time argued that the file wasn't really
needed then.  The attached proposed patch 0001 removes this obsolete file
and its references.

Of course, I was only looking at systemv in the first place because I'd
also recalled that we're still distributing the pacificnew file, which has
caused some confusion every so often and has likewise generally outlived
its usefulness.  This led me to the related file yearistype.sh, which is
also unused, except as a default script to pass to the Makefile to process
the TYPE field of Rule lines.

Given that the TYPE field hasn't been used by tzdata since 2000f and has
been more formally deprecated since 2015f, the whole unused feature is ripe
for "spring cleaning".  The attached proposed patch 0002 completely drops
support for the TYPE field (marking it reserved for compatibility purposes)
and causes non-trivial use of the field or use of zic's -y option to error
(instead of warning as it has since 2017c).  It also removes the pacificnew
and yearistype.sh files that are no longer needed and updates documentation
accordingly.

I don't presently foresee any need to repurpose the nullified field down
the road, but this is the next step in allowing us to "reclaim" it in the
event that such a need should arise in the future.

--
Tim Parenti
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