x86/acpi: Remove unused extern declaration acpi_copy_wakeup_routine()

This is now unused, so can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/all/20230620094519.15300-1-yuehaibing%40huawei.com