This cleanup was slated for after the conversion of the runtime to Go.
Also improve type and function documentation.

Change-Id: I55a16b09e00cf701f246deb69e7ce7e3e04b26e7
Reviewed-on: https://go-review.googlesource.com/3393Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>