OPENJDK-3655 moved to using Cekit's artifacts feature for installing scripts into the images.

For the OSBS builder back-end, this is implemented by uploading the scripts as sources to the dist-git lookaside cache (and the artifacts checksums stored in /sources).

This has broken the generation of source containers, which do not support Brew sources files.

We need source containers more than we need the source to be clean and nice, so revert that change. The plan of attack in future might be to extend Cekit's OSBS back-end to (optionally) not use Brew's lookaside cache.