cmd/go: quiet some logging
cmd/go: quiet some logging

This should've been behind -v before but was missed.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5836046

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang