Remove obsolete registry hacks from PE scripts

As of win-xenbus commit d916650 ("Merge pull request #33 from
mcb30/offline"), it is no longer necessary to guess the correct
ActiveDevice or to fake device counts.

Signed-off-by: Michael Brown <mbrown@fensystems.co.uk>
Merge pull request #86 from mcb30/offline

Remove obsolete registry hacks from PE scripts