runtime: remove unnecessary locking
runtime: remove unnecessary locking

R=rsc, dvyukov
CC=golang-dev
http://codereview.appspot.com/4819051

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go