lib/time, time/tzdata: update to 2021e

Doing this a little early in the release cycle as there have been some
changes in the handling of old timezones. They should continue to
work as expected, but more testing time may be useful.

For #22487

Change-Id: I3686fed79a052c46112445055044cff5842f2a45
Reviewed-on: https://go-review.googlesource.com/c/go/+/362874


Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>