xen: Remove stale irq_chip.end

irq_chip.end got obsolete with the removal of __do_IRQ()

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>