fix prowlarr exporter

Author: Mafyuh

docker/grafana/docker-compose.yml

@@ -76,7 +76,6 @@ services:
       URL: $PROWLARR_URL
       APIKEY: $PROWLARR_API
       PROWLARR__BACKFILL: true 
-      PROWLARR__BACKFILL_SINCE_DATE: "2023-03-01"
     ports:
      - "9710:9710"
     restart: unless-stopped