Remove unused package sources

Author: bording

nuget.config

@@ -2,7 +2,5 @@
 <configuration>
   <packageSources>
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
-    <add key="CodeGeneration.Roslyn" value="https://ci.appveyor.com/nuget/codegeneration-roslyn" />
-    <add key="corefxlab" value="https://dotnet.myget.org/F/dotnet-corefxlab/api/v3/index.json" />
   </packageSources>
 </configuration>