remove the no longer needed pid_alive() check in __task_pid_nr_ns()

Starting from 2c470475 ("pids: Move the pgrp and session pid pointers
from task_struct to signal_struct") __task_pid_nr_ns() doesn't dereference
task->group_leader, we can remove the pid_alive() check.

pid_nr_ns() has to check pid != NULL anyway, pid_alive() just adds the
unnecessary confusion.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

kernel/pid.c

@@ -495,7 +495,6 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
 	rcu_read_lock();
 	if (!ns)
 		ns = task_active_pid_ns(current);
-	if (likely(pid_alive(task)))
 	nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
 	rcu_read_unlock();