powerpc/mm: drop __bad_pte()

This has never been called (since Kernel has been in git at least),
drop it.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/nohash/32/pgalloc.h

@@ -22,8 +22,6 @@
  */
 #define MAX_PGTABLE_INDEX_SIZE	0xf
 
-extern void __bad_pte(pmd_t *pmd);
-
 extern struct kmem_cache *pgtable_cache[];
 #define PGT_CACHE(shift) pgtable_cache[shift]