Remove auditSources from NuGet.config (#368)

The api.nuget.org source will clash with the CFSClean network isolation policy

Author: akoeplinger

NuGet.config

@@ -6,10 +6,6 @@
     <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" />
     <add key="dotnet-tools" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json" />
   </packageSources>
-  <auditSources>
-    <clear />
-    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
-  </auditSources>
   <disabledPackageSources>
     <clear />
   </disabledPackageSources>