Remove "Stage" variable

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

deploy/grafana-dashboard/queries/requests-per-minute.flux

@@ -4,7 +4,6 @@ data = from(bucket: "poseidon")
   |> range(start: date.truncate(t: v.timeRangeStart, unit: 1m), stop: date.truncate(t: v.timeRangeStop, unit: 1m))
   |> 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", "status"])
 
 all = data |> set(key: "status", value: "all")