Remove unused functions spotted by honnef.co/go/unused.

Change-Id: Iabf3b201215ce21e420a60f4ef2679b36231eda7
Reviewed-on: https://go-review.googlesource.com/29132
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>