ptrace: s/tracehook_tracer_task()/ptrace_parent()/

tracehook.h is on the way out.  Rename tracehook_tracer_task() to
ptrace_parent() and move it from tracehook.h to ptrace.h.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index c825c6e..7312bf9 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -67,7 +67,7 @@
 	int error = 0;
 
 	rcu_read_lock();
-	tracer = tracehook_tracer_task(task);
+	tracer = ptrace_parent(task);
 	if (tracer) {
 		/* released below */
 		cred = get_task_cred(tracer);