Remove unused nuget feeds (#16878)

* Remove unused nuget feeds

* Add dotnet-core back

* dotnet-tools -> dotnet-eng

Author: wtgodbe

NuGet.config

@@ -8,10 +8,9 @@
     <add key="darc-pub-dotnet-corefx-4ac4c03" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/darc-pub-dotnet-corefx-4ac4c036/nuget/v3/index.json" />
     <!--End: Package sources managed by Dependency Flow automation. Do not edit the sources above.-->
     <add key="dotnet-core" value="https://dotnetfeed.blob.core.windows.net/dotnet-core/index.json" />
-    <add key="dotnet-tools" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json" />
+    <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" />
     <add key="dotnet3" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet3/nuget/v3/index.json" />
     <add key="dotnet3-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet3-transport/nuget/v3/index.json" />
-    <add key="aspnetcore-dev" value="https://dotnet.myget.org/F/aspnetcore-dev/api/v3/index.json" />
     <add key="grpc-nuget-dev" value="https://grpc.jfrog.io/grpc/api/nuget/v3/grpc-nuget-dev" />
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
   </packageSources>