[Backport 6.0.x] fix(sourcegraph): do not render SSLMODE twice for grafana sts (#628)

regression from
#617

it's now rendering `_SSLMODE` twice in the grafana sts

### Checklist

- [ ] Follow the [manual testing
process](https://github.com/sourcegraph/deploy-sourcegraph-helm/blob/main/TEST.md)
- [ ] Update
[changelog](https://github.com/sourcegraph/deploy-sourcegraph-helm/blob/main/charts/sourcegraph/CHANGELOG.md)
- [ ] Update [Kubernetes update
doc](https://docs.sourcegraph.com/admin/updates/kubernetes)

### Test plan

CI <br> Backport bb2d4f1 from #627

Co-authored-by: Michael Lin <[email protected]>

Author: sourcegraph-release-bot

charts/sourcegraph/templates/_helpers.tpl

@@ -216,13 +216,6 @@ app.kubernetes.io/name: jaeger
     secretKeyRef:
       key: sslmode
       name: {{ $secretName }}
-{{- if eq $service "grafana" }}
-- name: {{ printf "%sSSLMODE" $prefix }}
-  valueFrom:
-    secretKeyRef:
-      key: sslmode
-      name: {{ $secretName }}
-{{- end }}
 {{- end }}
 
 {{- define "sourcegraph.dataSource" -}}