Deprecate package `@azure/arm-deploymentmanager`

<img width="849" height="371" alt="Image" src="https://github.com/user-attachments/assets/12eeac0c-bf76-45ac-927d-7bb356575fe5" />

https://github.com/Azure/azure-rest-api-specs/pull/26818
from this spec pr. the specification was deleted 2 years ago, we need to launch the SDK retirement for deployment manager as well. 