Windows Install: Do not install the policy on XP

A bug in Fusion on XP causes downlevel issues with upgrade.  The long
term fix is to duplicate the Fusion behavior.  For now we just suppress
the install on XP
Revert "Windows: Skip policy assembly for now"

This reverts commit a759e5091f9cfb8921ac42d7b9bf1682c7943b75.

The policy assembly is now skipped on XP from within the policy assembly
itself so it can be safely installed elsewhere.