ghost-en: drop dead ghost-en-smtp ignoreDifferences (3c)

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

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

argocd/application-ghost-en.yaml

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