Type values being comparable implies that Type is a valid map key type.
As previously written, they sound unrelated.

Change-Id: I8e2235275d62898bfb47de850e8257b51ab5cbd6
Reviewed-on: https://go-review.googlesource.com/87021
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>