With the removal of the old backend,
a Label is just a Node.

Passes toolstash -cmp.

Change-Id: Ia62cb00fbc551efb75a4ed4dc6ed54fca0831dbf
Reviewed-on: https://go-review.googlesource.com/32216
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>