x86/topology: use weak version of arch_unregister_cpu()

Since the x86 version of arch_unregister_cpu() is the same as the weak
version, drop the x86 specific version.
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/E1r5R3r-00Cszs-2R@rmk-PC.armlinux.org.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kernel/topology.c

@@ -43,9 +43,4 @@ int arch_register_cpu(int cpu)
 	c->hotpluggable = cpu > 0;
 	return register_cpu(c, cpu);
 }
-
-void arch_unregister_cpu(int num)
-{
-	unregister_cpu(&per_cpu(cpu_devices, num));
-}
 #endif /* CONFIG_HOTPLUG_CPU */