Found by github.com/mvdan/unparam.

Change-Id: Ic97f05a2ecb5b17caa36aafe403e2266abea3e0e
Reviewed-on: https://go-review.googlesource.com/37836
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>