mm, memory_hotplug: remove obsolete generic_free_nodedata()

Commit 390511e1

 ("mm, memory_hotplug: drop arch_free_nodedata") drops
the last caller of generic_free_nodedata().  Remove it too.

Link: https://lkml.kernel.org/r/20220916072257.9639-11-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>