m68knommu: remove extern declarations of memory_start/memory_end from mm/init

We do not need to have local extern declarations of memory_start and
memory_end in mm/init_no.c. There are declarations already in asm/page_no.h.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>

arch/m68k/mm/init_no.c

@@ -45,9 +45,6 @@
  */
 void *empty_zero_page;
 
-extern unsigned long memory_start;
-extern unsigned long memory_end;
-
 /*
  * paging_init() continues the virtual memory environment setup which
  * was begun by the code in arch/head.S.