time/tzdata: generate zip constant during cmd/dist

time/tzdata: generate zip constant during cmd/dist

We have a make.bash-time generation capability,
so use it to generate the embedded zip file for time/tzdata.
This is one less file to try to review in CLs like CL 455356.

For #22487.
Fixes #43350.

Change-Id: I2fcd0665fa0b1c830baec5fb4cd714483fea25a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/455357
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>