xen/setup/pm/acpi: Remove the call to boot_option_idle_override.

We needed that call in the past to force the kernel to use
default_idle (which called safe_halt, which called xen_safe_halt).

But set_pm_idle_to_default() does now that, so there is no need
to use this boot option operand.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/setup.c

@@ -420,7 +420,6 @@ void __init xen_arch_setup(void)
 	boot_cpu_data.hlt_works_ok = 1;
 #endif
 	disable_cpuidle();
-	boot_option_idle_override = IDLE_HALT;
 	WARN_ON(set_pm_idle_to_default());
 	fiddle_vdso();
 }