[logdog] Fix metric collection
[logdog] Fix metric collection

LogDog was passing in invalid fields, and since https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/896328/
it results in a panic.

Also remove an unused metric.

Change-Id: I39ed736853b86446decfdb65bcd8863b33c88a51
Reviewed-on: https://chromium-review.googlesource.com/c/1472110
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>
Commit-Queue: Ryan Tseng <2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org>

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