remove nuget reference

Author: adstep

source/NuGet.config

@@ -4,7 +4,6 @@
     <!-- remove any machine-wide sources with <clear/> -->
     <clear />
     <add key="AdaptiveCards-Dependencies" value="https://pkgs.dev.azure.com/shine-oss/AdaptiveCards/_packaging/AdaptiveCards-Dependencies/nuget/v3/index.json" />
-    <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
   <disabledPackageSources>
     <clear />