Users/vnbaaij/more release prep (microsoft#3663)

* Remove extra feed

* Remove package source mapping to try and get ADO build going again

Author: vnbaaij

NuGet.config

@@ -4,9 +4,4 @@
     <clear />
     <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
   </packageSources>
-  <packageSourceMapping>
-    <packageSource key="dotnet-public">
-      <package pattern="*" />
-    </packageSource>
-  </packageSourceMapping>
 </configuration>