arm64: mm: Drop dead code for pud special bit handling

arm64: mm: Drop dead code for pud special bit handling

Keith Busch observed some incorrect macros defined in arm64 code [1].

It turns out the two lines should never be needed and won't be exposed to
anyone, because aarch64 doesn't select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD,
hence ARCH_SUPPORTS_PUD_PFNMAP is always N.  The only archs that support
THP PUDs so far are x86 and powerpc.

Instead of fixing the lines (with no way to test it..), remove the two
lines that are in reality dead code, to avoid confusing readers.

Fixes tag is attached to reflect where the wrong macros were introduced,
but explicitly not copying stable, because there's no real issue to be
fixed.  So it's only about removing the dead code so far.

[1] https://lore.kernel.org/all/Z9tDjOk-JdV_fCY4@kbusch-mbp.dhcp.thefacebook.com/#t

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Donald Dutile <ddutile@redhat.com>
Cc: Will Deacon <will@kernel.org>
Fixes: 3e509c9b03f9 ("mm/arm64: support large pfn mappings")
Reported-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Donald Dutile <ddutile@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250320183405.12659-1-peterx@redhat.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>