dotnetfeed deprecation

The feature using dotnetfeed.blob.core.windows.net was deprecated some years ago. The storage account using this is now being decommissioned. The storage account has hosted packages for a long time, but most packages from the feed are now either out of support, were only previews of now publicly-available versions, or have been migrated to nightly feeds or [nuget.org](http://nuget.org/).

## User Remediation
If the package is publicly supported, look for the package in [nuget.org](http://nuget.org/).