pid_ns: kill the now unused task_child_reaper()

task_child_reaper() has no callers anymore, kill it.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/pid_namespace.h

@@ -84,12 +84,6 @@ static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 	return tsk->nsproxy->pid_ns;
 }
 
-static inline struct task_struct *task_child_reaper(struct task_struct *tsk)
-{
-	BUG_ON(tsk != current);
-	return tsk->nsproxy->pid_ns->child_reaper;
-}
-
 void pidhash_init(void);
 void pidmap_init(void);