kernel: Remove unused z_ready_thread_locked()

Removing the routine z_ready_thread_locked() as it is not
used anywhere. It was a leftover artefact from development
that previously escaped cleanup.

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>
diff --git a/kernel/include/ksched.h b/kernel/include/ksched.h
index e82d1d1..b832fda 100644
--- a/kernel/include/ksched.h
+++ b/kernel/include/ksched.h
@@ -60,7 +60,6 @@
 void z_sched_ipi(void);
 void z_sched_start(struct k_thread *thread);
 void z_ready_thread(struct k_thread *thread);
-void z_ready_thread_locked(struct k_thread *thread);
 void z_requeue_current(struct k_thread *curr);
 struct k_thread *z_swap_next_thread(void);
 void z_thread_abort(struct k_thread *thread);
diff --git a/kernel/sched.c b/kernel/sched.c
index f55b2f8..f8d734f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -389,13 +389,6 @@
 	}
 }
 
-void z_ready_thread_locked(struct k_thread *thread)
-{
-	if (thread_active_elsewhere(thread) == NULL) {
-		ready_thread(thread);
-	}
-}
-
 void z_ready_thread(struct k_thread *thread)
 {
 	K_SPINLOCK(&_sched_spinlock) {