Remove attribute((unused) from sched_dequeue_task()

The function will be invoked in subsequent commits, so the
__attribute__((unused)) annotation is no longer appropriate.
Removing it cleans up the declaration and avoids misleading
annotations. No functional change.

Author: vicLin8712

kernel/task.c

@@ -387,7 +387,7 @@ static void sched_enqueue_task(tcb_t *task)
 }
 
 /* Remove task from ready queue; return removed ready queue node */
-static __attribute__((unused)) list_node_t *sched_dequeue_task(tcb_t *task)
+static list_node_t *sched_dequeue_task(tcb_t *task)
 {
     if (unlikely(!task))
         return NULL;