undo changes to NuGet.config from PR#887 (#888)

Author: anjbur

NuGet.config

@@ -11,8 +11,6 @@
 -->
 <configuration>
   <packageSources>
-    <clear />
     <add key="qdk-alpha" value="https://pkgs.dev.azure.com/ms-quantum-public/Microsoft Quantum (public)/_packaging/alpha/nuget/v3/index.json" protocolVersion="3" />
-    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>