Revert "Fix incorrect argument handling for expire in NodeExpirer"

This reverts commit 1c9bec019e08ce7f53d9fb8c9e7c7b23cc7c8bca. That changeset
was based on a misunderstanding of the code. NodeExpirer#save has an instance
of Puppet::Node::Facts but is calling xpire on Puppet::Node, so it's never
appropriate to pass along the instance.