`source-build-externals` repo should create packages in common folders

[NikolaMilosavljevic]

source-build-externals repo creates packages in Release sub-folder, instead of common Shipping and NonShipping - dotnet/source-build-externals#275 (comment)

Because of this, we needed a custom publishing infra: dotnet/source-build-externals#275

When this is fixed, custom publishing infra should be deleted.