Remove "Stage" variable

as we will use distinct Influx and Grafana instances for the different stages/environments.

deploy/grafana-dashboard/queries/request-latency.flux

@@ -2,6 +2,5 @@ from(bucket: "poseidon")
   |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
   |> filter(fn: (r) => r["_field"] == "duration")
   |> filter(fn: (r) => (not exists r.environment_id) or contains(value: r["environment_id"], set: ${environment_ids:json}))
-  |> filter(fn: (r) => (not exists r.stage) or contains(value: r["stage"], set: ${stages:json}))
   |> keep(columns: ["_time", "_value"])
   |> aggregateWindow(every: v.windowPeriod, fn: mean)