exit: Stop exporting do_exit

Now that there are no more modular uses of do_exit remove the EXPORT_SYMBOL.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

kernel/exit.c

@@ -843,7 +843,6 @@ void __noreturn do_exit(long code)
 	lockdep_free_task(tsk);
 	do_task_dead();
 }
-EXPORT_SYMBOL_GPL(do_exit);
 
 void __noreturn make_task_dead(int signr)
 {