ACPI: button: Remove unused acpi_lid_notifier_[un]register() functions

There are no users of the acpi_lid_notifier_[un]register functions,
so lets remove them.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>