Saves 22KB of memory in stdlib packages.

Updates #26775

Change-Id: Ia19fe7aff61f6e2ddd83cd35969d7ff94526591f
Reviewed-on: https://go-review.googlesource.com/127661
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>