mm, arch: remove empty_bad_page*

empty_bad_page() and empty_bad_pte_table() seem to be relics from old
days which is not used by any code for a long time.  I have tried to
find when exactly but this is not really all that straightforward due to
many code movements - traces disappear around 2.4 times.

Anyway no code really references neither empty_bad_page nor
empty_bad_pte_table.  We only allocate the storage which is not used by
anybody so remove them.

Link: http://lkml.kernel.org/r/20171004150045.30755-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Ralf Baechle <ralf@linus-mips.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: David Howells <dhowells@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/mem.c

@@ -22,8 +22,6 @@
 /* allocated in paging_init, zeroed in mem_init, and unchanged thereafter */
 unsigned long *empty_zero_page = NULL;
 EXPORT_SYMBOL(empty_zero_page);
-/* allocated in paging_init and unchanged thereafter */
-static unsigned long *empty_bad_page = NULL;
 
 /*
  * Initialized during boot, and readonly for initializing page tables
@@ -146,7 +144,6 @@ void __init paging_init(void)
 	int i;
 
 	empty_zero_page = (unsigned long *) alloc_bootmem_low_pages(PAGE_SIZE);
-	empty_bad_page = (unsigned long *) alloc_bootmem_low_pages(PAGE_SIZE);
 	for (i = 0; i < ARRAY_SIZE(zones_size); i++)
 		zones_size[i] = 0;