Remove AppVeyor

[HenriDeh]

If you check, all recent (not so recent anymore) are blocked due to a CI test failing on AppVeyor.
I don't have access to the detail (access denied). I used to, that's new.

It would be nice to find the commit that provoked this.

[oxinabox]

We don't use AppVeyor anymore. We are using GHA.
but only @kmsquire can remove it.
They said they would a few months back but they haven't

[oxinabox]

It doesn't actually block the PRs.
It is still possible to merge even with it failing.
It just means GH displays an annoying red cross

[kmsquire]

I thought I had removed that. Sorry, I’ll look again.

[kmsquire]

So, I had deleted the repository, and also removed the webhook. The reason for the access denied is because the project doesn't (or didn't) exist on AppVeyor.

I just recreated the project on AppVeyor (with a bad configuration) to see if I can debug.

[kmsquire]

It seems that the only way to get the error to go away is to push a new commit to each of these branches. Simply opening and closing the PR doesn't work.

appveyor/ci#3585 (comment)