Delete unused fields, methods, vars, and funcs. Spotted by
honnef.co/go/unused.

Change-Id: I0e65484bbd916e59369c4018be46f120b469d610
Reviewed-on: https://go-review.googlesource.com/27731
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>