Also, remove some test code that was trying to work on XP and fix up
some comments referencing XP.

Fixes #26191
Updates #23380

Change-Id: I0b7319fe1954afddb22d396e5ec91d8c960268d8
Reviewed-on: https://go-review.googlesource.com/123415
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>