Decommission Trickster for Grafana

• Trickster has been broken with Grafana since the upgrade to v8.3.6 (gitlab-com/gl-infra/k8s-workloads/tanka-deployments!314 (merged)
• It's only useful for caching when querying Prometheus directly, which should be avoided in favor of the Global datasource querying Thanos Query Frontend instead
• Thanos Query Frontend does a much better job at caching than Trickster