chore(argocd-understack): remove unnecessary ref in multi-source app

[cardoe]

Fast follow to #2205, addressing item 3 from the pass-4 review.

These ref: fields are never dereferenced — no source in these Applications uses $understack/ or $deploy/ in helm.valueFiles or anywhere else. Per 8f9e2d7 and 92ee95e, an unnecessary ref causes ArgoCD to crash with a runtime exception due to argoproj/argo-cd#25460, and that fix still has not been backported to any release branch.

Those two commits only covered the single-source Applications. This covers the multi-source ones that were missed:

Application	Removed
application-argo-events.yaml	ref: understack, ref: deploy
application-argo-events-workflows.yaml	ref: understack, ref: deploy
application-global-workflows.yaml	ref: understack, ref: deploy
application-openstack-sync-plugins.yaml	ref: understack, ref: deploy
application-external-secrets.yaml	ref: understack
application-openstack.yaml	ref: understack
application-snmp-exporter.yaml	the whole ref-only - ref: understack source

application-openstack.yaml keeps ref: deploy, which its valueFiles dereferences. application-snmp-exporter.yaml had a source consisting only of ref: understack with no path, referenced by nothing, so the source is dropped rather than just the ref. application-openstack-sync-operator.yaml keeps both of its refs since its helm.valueFiles dereferences each one.

Verification

Every ref: understack/ref: deploy in the chart was checked against whether its Application dereferences $understack//$deploy/. After this change no unused refs remain, and no Application references a ref it no longer declares.

Rendering charts/argocd-understack against both ci/example.yaml and ci/example-global.yaml, with all affected components enabled, gives 13 lines removed and 0 added versus main — only the ref: lines and the dead snmp-exporter source. No other manifest changes.

🤖 Generated with Claude Code