Remove the rootfses from the package registry after 60 days

According to upstream two months is fine:
tianon: yeah, cleaning them out is reasonable, although I'd request that
they be available for something like 1-2 months after they're no longer
supported / "active"
tianon: in the case of something constantly changing like arch, 1 month
is probably pretty reasonable

Fix #57 (closed)

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I suggest we add CLEANUP_PACKAGE_REGISTRY = TRUE to the weekly job.