prometheus: remove legacy config for bird

prometheus/files/prometheus/prometheus.yml

@@ -52,10 +52,6 @@ scrape_configs:
     file_sd_configs:
       - files:
           - /etc/prometheus/targets/bird.yml
-    metric_relabel_configs:
-      - source_labels: [__name__]
-        target_label: __name__
-        replacement: bird_${1}
 
   - job_name: grafana
     scheme: https