mm, swap: remove unused function prototype

This is a code cleanup patch, no functionality changes.  There are 2
unused function prototype in swap.h, they are removed.

Link: http://lkml.kernel.org/r/20170405071017.23677-1-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/swap.h

@@ -411,9 +411,6 @@ struct backing_dev_info;
 extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
 extern void exit_swap_address_space(unsigned int type);
 
-extern int get_swap_slots(int n, swp_entry_t *slots);
-extern void swapcache_free_batch(swp_entry_t *entries, int n);
-
 #else /* CONFIG_SWAP */
 
 #define swap_address_space(entry)		(NULL)