It's unused since https://golang.org/cl/99320043

Change-Id: I74d69ff894aa2fb556f1c2083406c118c559d91b
Reviewed-on: https://go-review.googlesource.com/98195
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>