[dasc] Renamed structured content keys are not removed from EDS JSON response

## Renamed structured content keys are not removed from EDS JSON response

## Issue
EDS structured content currently retains the old key when a field key is renamed.

Steps to Reproduce:

* Create a structured content field with key `employeeCommsManifest`.
* Rename the key to `employeeCommsConfig`.
* Publish/update the content.
* Inspect the JSON response.

## Current Behavior

The JSON response contains both:
```
{
"employeeCommsManifest": { ... },
"employeeCommsConfig": { ... }
}
```

The old key `employeeCommsManifest` remains in the response even after the rename.

## Expected Behavior

When a key is renamed, the old key should be removed from the generated JSON response. Only the new key should be present.

```
{
"employeeCommsConfig": { ... }
}
```

Start by reproducing the rename flow and inspect the code path that generates the EDS JSON response. Verify that after publish/update the response contains employeeCommsConfig and no employeeCommsManifest, then add regression coverage if the repository has a suitable existing test entry point.

Written by the indexing model from the issue text.