[cv] code cleanup
[cv] code cleanup

Follow-up changes for crrev.com/c/3339545

Change-Id: I0063734533f59d6abc56c8f96ed8e3c975556d65
Bug: 1268574
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3388346
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Commit-Queue: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

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