mm/page_alloc: Remove useless parameter of __free_pages_boot_core

__free_pages_boot_core has parameter pfn which is not used at all.
Remove it.

Signed-off-by: Li Zhang <zhlcindy@linux.vnet.ibm.com>
Reviewed-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>