Revert "deploy alerta on grafana.hosts.hamburg.ccc.de"

This reverts commit b10d7d1592.

resources/chaosknoten/grafana/docker_compose/alertmanager.yaml.j2

@@ -9,9 +9,6 @@ route:
   group_interval: 5m
   repeat_interval: 26h
   routes:
-    - receiver: alerta
-      matchers: {}
-      continue: true
     - receiver: "null"
       matchers:
         - sendAlert = "false"
@@ -76,8 +73,3 @@ receivers:
         smarthost: "cow.hamburg.ccc.de:587"
         auth_username: "alert-manager@hamburg.ccc.de"
         auth_password: {{ secret__alert_manager_email_password }}
-
-  - name: "alerta"
-    webhook_configs:
-      - url: "http://alerta.hamburg.ccc.de/webhooks/prometheus"
-        send_resolved: true