[S390] sysctl: get rid of dead declaration

Remove dead sysctl_userprocess_debug. The variable is
gone since we map our old userprocess_debug sysctl to
the common code show_unhandled_signals sysctl on s390.
Signed-off-by: NHeiko Carsten <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/system.h

@@ -20,8 +20,6 @@
 
 struct task_struct;
 
-extern int sysctl_userprocess_debug;
-
 extern struct task_struct *__switch_to(void *, void *);
 extern void update_per_regs(struct task_struct *task);