"Breaking Change(Cross-Version)" does not report on removal of model (which is not used in API)

CI in [PR](https://github.com/Azure/azure-rest-api-specs-pr/pull/11349)
does not report removal of [ContainerServiceVMSize](https://github.com/Azure/azure-rest-api-specs/blob/main/specification/containerservice/resource-manager/Microsoft.ContainerService/aks/stable/2023-01-01/managedClusters.json#L2629) from 2023-02-01 api-version.

It is acceptable this does not report as an Error, as the model is not used by current API. (it was used by old [ContainerService swagger](https://github.com/Azure/azure-rest-api-specs/blob/main/specification/containerservice/resource-manager/Microsoft.ContainerService/aks/stable/2017-07-01/containerService.json#L605))

However, on SDK perspective, would expect at least a Warning, when a model get removed from swagger.

Start with the CI result in PR 11349 and compare the 2023-02-01 managedClusters.json model removal with the older containerService.json definition. Trace the cross-version breaking-change check and determine how an unused model removal is classified; done means it reports at least a Warning without treating it as an Error.

Written by the indexing model from the issue text.