Remove Roslyn MyGet feeds (#27442) (#27550)

- neither of these should be needed anymore

NuGet.config

@@ -10,17 +10,11 @@
     <add key="darc-pub-dotnet-runtime-7ef6d50" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/darc-pub-dotnet-runtime-7ef6d50b/nuget/v3/index.json" />
     <!--  End: Package sources from dotnet-runtime -->
     <!--End: Package sources managed by Dependency Flow automation. Do not edit the sources above.-->
-    <!--  Begin: Package sources from dotnet-efcore -->
-    <!--  End: Package sources from dotnet-efcore -->
-    <!--  Begin: Package sources from dotnet-runtime -->
-    <!--  End: Package sources from dotnet-runtime -->
     <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/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="dotnet5" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json" />
     <add key="dotnet5-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5-transport/nuget/v3/index.json" />
-    <add key="roslyn" value="https://dotnet.myget.org/F/roslyn/api/v3/index.json" />
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
-    <add key="roslyn-tools" value="https://dotnet.myget.org/F/roslyn-tools/api/v3/index.json" />
     <!-- Used for the SiteExtension 3.1 bits that are included in the 5.0 build -->
     <add key="dotnet31-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet3.1-transport/nuget/v3/index.json" />
   </packageSources>