powerpc/book3s64: Avoid __pte_protnone() check in __pte_flags_need_flush()

This reverts commit 1abce058 ("powerpc/64s: Fix __pte_needs_flush()
false positive warning")

The previous patch dropped the usage of _PAGE_PRIVILEGED with PAGE_NONE.
Hence this check can be dropped.

Signed-off-by: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231204093638.71503-2-aneesh.kumar@kernel.org