zona-exclusion: drop dead zona-exclusion-secrets ignoreDifferences (3c)

Old out-of-band zona-exclusion-secrets deleted (kubectl); SMTP now sourced from
Infisical-backed zona-exclusion-secrets-infisical. Remove the obsolete /data
ignoreDifferences stanza from both app manifests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

argocd/application-zona-exclusion.yaml

@@ -9,13 +9,6 @@ spec:
   destination:
     namespace: zona-exclusion
     server: https://kubernetes.default.svc
-  ignoreDifferences:
-  - group: ''
-    jsonPointers:
-    - /data
-    kind: Secret
-    name: zona-exclusion-secrets
-    namespace: zona-exclusion
   project: default
   source:
     path: zona-exclusion