Replace spammy log message in dscache with comment.
Replace spammy log message in dscache with comment.

Fixes luci/gae#35.

R=dnj@chromium.org, estaab@chromium.org, martiniss@chromium.org, vadimsh@chromium.org
BUG=https://github.com/luci/gae/issues/35

Review URL: https://codereview.chromium.org/1556193002

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go