x86/mm: Drop pud_mknotpresent()

There is an inconsistency between PMD and PUD-based THP page table helpers
like the following, as pud_present() does not test for _PAGE_PSE.

pmd_present(pmd_mknotpresent(pmd)) : True
pud_present(pud_mknotpresent(pud)) : False

Drop pud_mknotpresent() as there are no current users. If/when needed
back later, pud_present() will also have to be fixed to accommodate
_PAGE_PSE.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lkml.kernel.org/r/1584925542-13034-1-git-send-email-anshuman.khandual@arm.com