Drop mmca prometheus federation

Thanos will be in charge of it from now on

Related to T4385

Test Plan

octo-diff:

  File[/etc/prometheus/prometheus.yml.base] =>
   parameters =>
     content =>
      @@ -7,18 +7,5 @@
           replica: '0'
       rule_files: []
      -scrape_configs:
      -- job_name: federate-mmca.softwareheritage.org
      -  honor_labels: true
      -  scheme: https
      -  metrics_path: "/prometheus/federate"
      -  basic_auth:
      -    username: prometheus
      -    password: prometheus
      -  params:
      -    match[]:
      -    - '{instance="mmca.internal.softwareheritage.org"}'
      -  static_configs:
      -  - targets:
      -    - mmca.softwareheritage.org
      +scrape_configs:_
       alerting:
         alert_relabel_configs: []
*******************************************
*** End octocatalog-diff on pergamon.softwareheritage.org

---

Migrated from D8143 (view on Phabricator)