[cv][cl] de-register legacy Gerrit CL queue.
[cv][cl] de-register legacy Gerrit CL queue.

This is entirely separate CL and ideally should be deployed
to prod w/o other changes.

R=yiwzhang

CL to disable alerts to the legacy queue: http://cl/419678927
Bug: 1281989
Change-Id: I93d082fb7aa507fe4f0884dca0eaec66aa3330f9
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3352342
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

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