cert-manager: Drop acmeDNS solver

ACME DNS seems to have stopped working (401 Unauthorized for all
requests).  I've migrated the rest of the domains to use Cloudflare.

cert-manager/cluster-issuer.yaml

@@ -21,21 +21,3 @@ spec:
           apiTokenSecretRef:
             name: cloudflare
             key: cloudflare.api-token
-    - dns01:
-        cnameStrategy: Follow
-        acmeDNS:
-          host: https://auth.acme-dns.io/
-          accountSecretRef:
-            name: acme-dns
-            key: acme-dns.json
-      selector:
-        dnsNames:
-        - pyrocufflink.blue
-        - '*.pyrocufflink.blue'
-        - pyrocufflink.net
-        - '*.pyrocufflink.net'
-        - dustin.hatch.name
-        - '*.dustin.hatch.name'
-        - aimee-os.org
-        - '*.aimee-os.org'
-        - '*.import.firefly.pyrocufflink.blue'