Merge in 'release/3.1' changes

Author: dotnet-bot

NuGet.config

@@ -9,14 +9,12 @@
   </packageRestore>
   <packageSources>
     <clear />
-    <add key="dotnet-coreclr" value="https://dotnetfeed.blob.core.windows.net/dotnet-coreclr/index.json" />
-    <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="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="dotnet3.1" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet3.1/nuget/v3/index.json" />
     <add key="dotnet3.1-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet3.1-transport/nuget/v3/index.json" />
-    <add key="myget-core-blob" value="https://dotnetmygetlegacy.blob.core.windows.net/dotnet-core/index.json" />
+    <add key="myget-legacy" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/myget-legacy/nuget/v3/index.json" />
     <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
     <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" />
   </packageSources>