nginx: remove a few fields from json_reduced

This brings it in line with the non-JSON reduced log format.

roles/prometheus/defaults/main.yml

@@ -75,6 +75,8 @@ blackbox_targets:
   smtp_starttls:
     - mail.archlinux.org:25
     - lists.archlinux.org:25
+  dns_geomirror_a: "{{ groups['geo_mirrors'] + ['mirror.pkgbuild.com'] }}"
+  dns_geomirror_aaaa: "{{ groups['geo_mirrors'] + ['mirror.pkgbuild.com'] }}"
 matrix_metrics_endpoints:
   - homeserver
   - appservice