Blackfin: remove unnecessary prototype for kobjsize()

The prototype for kobjsize() is already defined in linux/mm.h which is
included where kobjsize() is used.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bob Liu <lliubbo@gmail.com>

arch/blackfin/include/asm/pgtable.h

@@ -83,8 +83,6 @@ PTE_BIT_FUNC(mkyoung, |= _PAGE_ACCESSED);
 #define ZERO_PAGE(vaddr)	virt_to_page(empty_zero_page)
 extern char empty_zero_page[];
 
-extern unsigned int kobjsize(const void *objp);
-
 #define swapper_pg_dir ((pgd_t *) 0)
 /*
  * No page table caches to initialise.