m68knommu: 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: NTobias Klauser <tklauser@distanz.ch>
Signed-off-by: NGreg Ungerer <gerg@uclinux.org>

arch/m68k/include/asm/pgtable_no.h

@@ -45,11 +45,6 @@ static inline int pte_file(pte_t pte) { return 0; }
  */
 #define ZERO_PAGE(vaddr)	(virt_to_page(0))
 
-/*
- * These would be in other places but having them here reduces the diffs.
- */
-extern unsigned int kobjsize(const void *objp);
-
 /*
  * No page table caches to initialise.
  */