Remove obsolete package sources from NuGet.config

[joperezr]

These feeds are no longer needed for our packages, and they are causing build breaks on all CI, so removing them to fix the rest of the builds.

cc: @pgrawehr

Microsoft Reviewers: Open in CodeFlow

[pgrawehr]

Thank you!

But it seems this wasn't the full solution yet.

/home/vsts/work/1/s/src/Iot.Device.Bindings.SkiaSharpAdapter/Iot.Device.Bindings.SkiaSharpAdapter.csproj : error NU1101: Unable to find package Iot.Device.Bindings.SkiaSharpAdapter. No packages exist with this id in source(s): dotnet-eng, dotnet-public, dotnet-tools [/home/vsts/work/1/s/build.proj]
##[error]src/Iot.Device.Bindings.SkiaSharpAdapter/Iot.Device.Bindings.SkiaSharpAdapter.csproj(0,0): error NU1101: (NETCORE_ENGINEERING_TELEMETRY=Restore) Unable to find package Iot.Device.Bindings.SkiaSharpAdapter. No packages exist with this id in source(s): dotnet-eng, dotnet-public, dotnet-tools

Can it be that Iot.Device.Bindings.SkiaSharpAdapter was never properly uploaded to the internal feeds? It is available via nuget, though.

[joperezr]

I was expecting the first build to fail, I was mirroring that package to dotnet-public but that is done now so requeuing should work.

[joperezr]

Merging to unblock other PRs