This debugging print crept into an earlier CL of mine.

Change-Id: If6e8609e69a60aec50c06889c2d98a8b8a4bd02b
Reviewed-on: https://go-review.googlesource.com/18971
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>