The code was maintaining manual versions of it in multiple places -
replace all of them.

Change-Id: I04c3063877b05ba914de9f5dddb33ffe09f308fe
Reviewed-on: https://go-review.googlesource.com/95356
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>