lib/time, time, time/tzdata: use slim tz data format

Follow-up for CL 261363 which had to retain the fat tz data format due
to failing test.

The reason for the failed tests was that when caching location data, the
extended time format past the end of zone transitions was not
considered. The respective change was introduced in (*Location).lookup
by CL 215539.

This slims down zoneinfo.zip (and thus also the embedded copy in
time/tzdata) by ~350KB.

Change-Id: I412f79de98ba45358b8696aca784999b3479135e
Reviewed-on: https://go-review.googlesource.com/c/go/+/261877


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