debian: Revert back to using libxen-dev as depend

debian/control

@@ -2,7 +2,7 @@ Source: qubes-utils
 Section: admin
 Priority: extra
 Maintainer: Davíð Steinn Geirsson <david@dsg.is>
-Build-Depends: libvchan-xen-dev, libxen-qubes-vm-dev, debhelper (>= 8.0.0), quilt (>= 0.60), dh-systemd
+Build-Depends: libvchan-xen-dev, libxen-dev, debhelper (>= 8.0.0), quilt (>= 0.60), dh-systemd
 Standards-Version: 3.9.3
 Homepage: http://www.qubes-os.org
 Vcs-Git: http://dsg.is/qubes/qubes-linux-utils.git