cmd/gc/lex: remove reference to container/vector in comment
cmd/gc/lex: remove reference to container/vector in comment

R=golang-dev, dsymonds
CC=golang-dev
http://codereview.appspot.com/4921045
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go