[tz] [PATCH] Revert recent pre-1970 changes.

[Stephen Colebourne]

Here is the patch of reversions I would consider to be appropriate:
https://github.com/jodastephen/tz/commit/86a12cbb08b28683d964f0960c6453abbd1b70da

(I worked from the base 4c43a929191da9711045b8efe30bbdbbfb7e0bcb
commit. So, this can be examined against a git diff to that commit)

This reverts all problematic changes to antarctica, europe,
northamerica, southamerica, backward, zone.tab and Theory. (I believe
that the current git repo is incorrect in various ways following
previous partial reversions). This reversion should be checked before
being applied, as it has not been compiled/tested.

The Theory change reinstates the one zone per ISO-3166 region
requirement. This is because it is a solid requirement, long standing,
well understood and non political (if the ISO body deems an area to be
sufficiently important to give it a code, tzdb should deem it
important enough to give it a zone ID). I have not added any
requirement to have a full history per ISO-3166 at this point.

The associated checktab.awk check should also be reinstated, but I
didn't feel confident doing so without the ability to compile/run/test
it.

Where links have been re-added to the
europe/northamerica/southamerica/antarctic files, I have added a new
comment - "Same zone history as xxx/yyy, so share the data". This
comment is intended to defuse certain conflict boundary issues by
indicating that the link exists to share data, not for any other
reason. The right place for such links is in the main files, not the
backward file, as the backward file should be entirely optional (ie.
renames only).

I would note that this applying this reversion, and recent
discussions, imply a Theory rule around what the backward file is for.
ie. that the system should follow the Theory rules even if the
backward file is excluded from compilation.

thanks
Stephen