Failed to delete Security Center Assessment Policy

Recently we found service API failed to delete Security Center Assessment Policy with below error. Could you take a look this issue? Thanks.

Request payload:
```
DELETE https://management.azure.com/subscriptions/xx-xx-xxx-xxx/providers/Microsoft.Security/assessmentMetadata/xx-xx-xxx-xxx-xx
```

Error Message:
```
{
"status": {
"value": "Failed",
"localizedValue": "Failed"
},
"subStatus": {
"value": "InternalServerError",
"localizedValue": "Internal Server Error (HTTP Status Code: 500)"
},
"properties": {
"statusCode": "InternalServerError",
"statusMessage": "{\"error\":{\"code\":\"InternalServerError\",\"message\":\"\"}}",
"message": "Microsoft.Security/assessmentMetadata/delete"
}
}
```

Start by reproducing the DELETE request for the Microsoft.Security assessmentMetadata resource and inspect the corresponding Azure REST API specification. Done means determining whether the HTTP 500 is caused by the specification or the service, then recording the required follow-up or specification change.

Written by the indexing model from the issue text.