pidfd: kill the no longer needed do_notify_pidfd() in de_thread()

Now that __change_pid() does wake_up_all(&pid->wait_pidfd) we can kill
do_notify_pidfd(leader) in de_thread(), it calls release_task(leader)
right after that and this implies detach_pid(leader, PIDTYPE_PID).

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240202131248.GA26022@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: oleg-nesterov

fs/exec.c

@@ -1143,11 +1143,6 @@ static int de_thread(struct task_struct *tsk)
 
 		BUG_ON(leader->exit_state != EXIT_ZOMBIE);
 		leader->exit_state = EXIT_DEAD;
-		/*
-		 * leader and tsk exhanged their pids, the old pid dies,
-		 * wake up the PIDFD_THREAD waiters.
-		 */
-		do_notify_pidfd(leader);
 		/*
 		 * We are going to release_task()->ptrace_unlink() silently,
 		 * the tracer can sleep in do_wait(). EXIT_DEAD guarantees