MAINTAINERS: update XEN HYPERVISOR INTERFACE

I am no longer in a postion to be a maintainer of the Xen subsystem.
Signed-off-by: NDavid Vrabel <david.vrabel@citrix.com>
Acked-by: NJuergen Gross <jgross@suse.com>
Acked-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: NJuergen Gross <jgross@suse.com>

MAINTAINERS

@@ -13195,7 +13195,6 @@ F:	drivers/media/tuners/tuner-xc2028.*
 
 XEN HYPERVISOR INTERFACE
 M:	Boris Ostrovsky <boris.ostrovsky@oracle.com>
-M:	David Vrabel <david.vrabel@citrix.com>
 M:	Juergen Gross <jgross@suse.com>
 L:	xen-devel@lists.xenproject.org (moderated for non-subscribers)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git