Remove code host rate limit critical alerts
Created by: michaellzc
Part of https://github.com/sourcegraph/sourcegraph/issues/36434 to clean up critical alerts that are not worth waking a site admin up at night.
This alert get trigger quite frequently on managed instances, especially when customers are running large batch changes https://sourcegraph.slack.com/archives/C017SLJGA2Z/p1659432203371909
If we're running into rate limiting issue, we should instead show a warning notification from the admin UI.
Test plan
CI