Fix a compile error due to unused import introduced by CL 154663.

Change-Id: I2a732380c35cd98dfff36289f5d72fd7d7222205
GitHub-Last-Rev: 5c7065d26c8bf85d5dd7dc74f1631ab3532f69a9
GitHub-Pull-Request: golang/sys#26
Reviewed-on: https://go-review.googlesource.com/c/155460Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>