rpm: do not motify /etc/udev/rules.d/xen-backend.rules anymore
rpm: do not motify /etc/udev/rules.d/xen-backend.rules anymore

Xen 4.6 no longer uses udev to call hotplug scripts.

QubesOS/qubes-issues#1361

QubesOS/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin