AppVeyor builds have stopped

[dhermes]

The last build on https://ci.appveyor.com/project/GoogleCloudPlatform/google-cloud-python/history was 20 days ago.

I searched through issues to see if there was a discussion but I couldn't find one.

[busunkim96]

If we begin windows testing it will most likely be through Kokoro, not AppVeyor. Closing as obsolete.