PCI: Remove unused and broken to_hotplug_slot()

to_hotplug_slot() is unused and wouldn't work anyway, because struct
hotplug_slot no longer contains a struct kobject (it was removed by
f46753c5 ("PCI: introduce pci_slot")).

Remove to_hotplug_slot().

[bhelgaas: changelog]
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

include/linux/pci_hotplug.h

@@ -109,7 +109,6 @@ struct hotplug_slot {
 	struct list_head		slot_list;
 	struct pci_slot			*pci_slot;
 };
-#define to_hotplug_slot(n) container_of(n, struct hotplug_slot, kobj)
 
 static inline const char *hotplug_slot_name(const struct hotplug_slot *slot)
 {