It's unused and doesn't work.

Fixes #20833

Change-Id: I09335e84c60f88dd1771f7353b0097f36a5e7660
Reviewed-on: https://go-review.googlesource.com/82636
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>