[POWERPC] Remove DISCONTIGMEM cruft from page.h

This looks like cruft to me, these functions don't exist AFAICT,
and I can't see that it's possible to even enable DISCONTIGMEM on
powerpc anymore. CC'ing some folks who might know better, based on
the who-touched-it-last principle.

Signed-off-by: Michael Ellerman <[e-mail]>
Signed-off-by: Paul Mackerras <[e-mail]>

include/asm-powerpc/page.h

···
 #define PAGE_OFFSET     ASM_CONST(CONFIG_KERNEL_START)
 #define KERNELBASE      (PAGE_OFFSET + PHYSICAL_START)
 
-#ifdef CONFIG_DISCONTIGMEM
-#define page_to_pfn(page)	discontigmem_page_to_pfn(page)
-#define pfn_to_page(pfn)	discontigmem_pfn_to_page(pfn)
-#define pfn_valid(pfn)		discontigmem_pfn_valid(pfn)
-#endif
-
 #ifdef CONFIG_FLATMEM
 #define pfn_valid(pfn)		((pfn) < max_mapnr)
 #endif