remove orphaned platform-api-server gitlinks (#1132)

## Summary

- Remove orphaned `160000` gitlink entries for both
`platform-api-server` and `platform-control-plane` that were
accidentally introduced by the automated merge script in commit
`adc3b9c2`
- There are no corresponding `.gitmodules` configurations, so these
entries are dangling and cause kustomize/ArgoCD to fail when processing
the repository tree

## Details

Both gitlinks pointed to commits in submodules that do not exist in this
repository:

| Gitlink | Commit |
|---------|--------|
| `platform-api-server` | `936ea12b22ab15a12657f6aa89eeb0c19f41c191` |
| `platform-control-plane` | `4dae05c6ef8e4e4ef74bfe3c4b1c86467fb1f516`
|

These broke deployments on the `alpha` branch because kustomize and
ArgoCD cannot resolve the references.

Fixes #1130

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: ktdreyer