Remove obsolete AzureAd

[HaoK]

Part of #27529

[Tratcher]

There's a lot of discussion on #27529 about if removing these APIs is actually necessary. Yes they've been replaced, but the old ones still work so do we need to forcibly break people that are still using them?

Is there a clear functional problem here driving the removal?

[HaoK]

These have been a constant source of issues and errors, doesn't an LTS seem like a good time to encourage them to move to the intended final destination? Basically bullet 2

What's the maintenance cost of keeping the API around? This includes things like the number of issues reported by users, whether there's a lot of flaky tests associated with the API, etc.

[HaoK]

This seems analogous to our Azure Key Vault configuration provider which we also dropped rather than keeping around with obsolete since its an externally owned feature

[Tratcher]

We already moved the templates so that should cut down on the incoming issues. The main concern is if we're forcing change on people who weren't broken. That's @blowdart's call.

[HaoK]

Right, I checked with @blowdart before opening the PR :)

[blowdart]

I lean on kill it off, obviously. People do need to change, because the v1 endpoint will retire, probably before the LTS expiry. Same with the app creation API.

[blowdart]

This apparently needs a wider discussion :)

[Tratcher]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[HaoK]

@blowdart did we get everything straightened out on the process side on your end for approval?

[blowdart]

We did not. The thread is ongoing. I'll ressurect it. We may have to keep it for a while longer.

[blowdart]

Closing until v7