Fixup feeds (#1982)

Co-authored-by: Matt Mitchell <[email protected]>

Author: dotnet-bot

NuGet.config

@@ -12,11 +12,8 @@
     <add key="dotnet5-transport" value="https://dnceng.pkgs.visualstudio.com/public/_packaging/dotnet5-transport/nuget/v3/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" />
-    <!-- Legacy feeds -->
-    <add key="dotnet-buildtools" value="https://dotnet.myget.org/F/dotnet-buildtools/api/v3/index.json" />
-    <add key="dotnet-core" value="https://dotnetfeed.blob.core.windows.net/dotnet-core/index.json" />
-    <!-- Standard feeds -->
-    <add key="nuget.org" value="https://api.nuget.org/v3/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" />
   </packageSources>
   <disabledPackageSources />
 </configuration>