Removal of older Functions runtime version: 3.21.0

[VpOfEngineering]

Older versions of Azure Functions are regularly removed from the production environment. Going forward we will be using issues in this repo to announce when that is happening. The following versions of Azure Functions V3 are being removed from the production environment.

- 3.21.0

If your function app is configured to run on any of these versions (using the FUNCTIONS_EXTENSION_VERSION app setting) you will soon find that the app is instead loading the latest version automatically.

Please use Azure/app-service-announcements-discussions#355 for discussions related to the removal of these versions.