mm: remove checks for pte_index

Since pte_index is always defined, we don't need to check whether it's
defined or not.  Delete the slow version that doesn't depend on it and
remove the #define since nobody needs to test for it.

Link: https://lkml.kernel.org/r/20230819031837.3160096-1-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Christian Dietrich <stettberger@dokucode.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>