Remove one useless extern declaration

The file exit.c contains one useless extern declaration of sem_exit().
Moreover, it refers to nothing.

This trivial patch removes it.
Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Signed-off-by: Adrian Bunk <bunk@kernel.org>

kernel/exit.c

@@ -50,8 +50,6 @@
 #include <asm/pgtable.h>
 #include <asm/mmu_context.h>
 
-extern void sem_exit (void);
-
 static void exit_mm(struct task_struct * tsk);
 
 static void __unhash_process(struct task_struct *p)