unicode/bidi: remove vet complaint

Change-Id: Ia179c919ecafbeeccb916abbcf553fc3a204dcfb
Reviewed-on: https://go-review.googlesource.com/38360
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed