Revert "pmb.install.losetup: Run kpartx, losetup in chroot (MR 2430)"

This series breaks pmbootstrap, and that's not good[1]. A bug was filed about this (#2465 (closed)), and there have been multiple attempts to fix it (!2435 (closed) and !2436 (closed)). It kinda seems like we don't have time to fix/test this for a while longer, which is fine, but given the impact this bug has I think we should be revert this series until this issue is solved/tested.

1. pmb is broken in some specific cases, which means some workflows are broken. One example is that this breaks the pmaports CI, so no work can be done in pmaports.