Delete unused NuGet source (#51365)

Author: mthalman

NuGet.config

@@ -58,7 +58,6 @@
     <add key="vs-impl" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vs-impl/nuget/v3/index.json" />
     <!-- Used for Rich Navigation indexing task -->
     <add key="richnav" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vs-buildservices/nuget/v3/index.json" />
-    <!-- <add key="darc-int-DotNet-msbuild-Trusted-728984d" value="true" /> -->
   </packageSources>
   <disabledPackageSources>
     <!--Begin: Package sources managed by Dependency Flow automation. Do not edit the sources below.-->