Revert "Allow specifying packages whose closures should be in the chroot"

This reverts commit be3d498b1891339ffceb3f54f749d3d5fa343429.
Revert "Only include /bin/sh (not all of /bin) in the chroot"

This reverts commit 883d310bac6cc6b7a136786688b6b55079558cb7.