remove references to deprecated service 'Azure Spatial Anchors' (Azure#39405)

Author: pamistel

sdk/mixedreality/azure-mixedreality-authentication/README.md

@@ -2,12 +2,10 @@
 
 # Azure Mixed Reality Authentication Package client library for Python
 
-Mixed Reality services, like Azure Spatial Anchors, Azure Remote Rendering, and others, use the Mixed Reality security
+Mixed Reality services, like Azure Remote Rendering use the Mixed Reality security
 token service (STS) for authentication. This package supports exchanging Mixed Reality account credentials for an access
 token from the STS that can be used to access Mixed Reality services.
 
-![Mixed Reality service authentication diagram](https://docs.microsoft.com/azure/spatial-anchors/concepts/media/spatial-anchors-authentication-overview.png)
-
 # Getting started
 
 ## Currently supported environments
@@ -19,7 +17,6 @@ This package has been tested with Python 3.7+.
 - An [Azure subscription][azure_sub].
 - You must have an account with an [Azure Mixed Reality service](https://azure.microsoft.com/topic/mixed-reality/):
   - [Azure Remote Rendering](https://docs.microsoft.com/azure/remote-rendering/)
-  - [Azure Spatial Anchors](https://docs.microsoft.com/azure/spatial-anchors/)
 - Familiarity with the authentication and credential concepts from the [Azure Identity library][azure_identity].
 - Python 3.7 or later is required to use this package.
 
@@ -195,5 +192,4 @@ build and test the code.
 [azure_sub]: https://azure.microsoft.com/free/
 [azure_portal]: https://portal.azure.com
 [azure_identity]: https://github.com/Azure/azure-sdk-for-python/tree/main/sdk/identity/azure-identity
-[register_aad_app]: https://docs.microsoft.com/azure/spatial-anchors/concepts/authentication
 [defaultazurecredential]: https://github.com/Azure/azure-sdk-for-python/tree/main/sdk/identity/azure-identity#defaultazurecredential