[tz] Undoing the effect of the new alike-since-1970 patch

[Paul Eggert]

On 6/6/21 1:07 AM, Stephen Colebourne via tz wrote:

> rearguard did not solve the problem
> in 2018. Downstream projects were still forced to change their code.

They were not forced to. They could have used (and still can use) the 
Makefile to generate files in the format they prefer. This generation 
process doesn't need to be done in Java; it can be done offline on any 
POSIX platform, and the result can be redistributed and given to 
whatever Java code still requires rearguard format.

If that process is too much trouble for downstream users, we can arrange 
to generate the alternate source upstream. For example, we could ship a 
tarball with an altered tzdata.zi file (this is what Tom suggested).