ptrace: kill task_ptrace()

task_ptrace(task) simply dereferences task->ptrace and isn't even used
consistently only adding confusion.  Kill it and directly access
->ptrace instead.

This doesn't introduce any behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

mm/oom_kill.c

@@ -339,8 +339,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
 				 * then wait for it to finish before killing
 				 * some other task unnecessarily.
 				 */
-				if (!(task_ptrace(p->group_leader) &
-							PT_TRACE_EXIT))
+				if (!(p->group_leader->ptrace & PT_TRACE_EXIT))
 					return ERR_PTR(-1UL);
 			}
 		}