Fix endpoints by urgency dashboard

https://dashboards.gitlab.net/d/general-request-apdex-sli-adoption/general-request-apdex-participation?orgId=1

This dashboard was previously used for getting teams to opt into using the new thresholds but is no longer working. We don't need the "opted in" information any more, but the information about endpoints/traffic by urgency is helpful.

Edited by Rachel Nienaber