Move unschedulable Pod to internal schedulingQ synchronously

- use in-cache Pod instead of real-time Pod (by calling API server) to mark it as unschedulable
  in internal schedulingQ
- remove the backoff logic as now we don't call API server
- the whole logic is changed to a synchronous call

pkg/scheduler/internal/queue/scheduling_queue.go

@@ -563,7 +563,7 @@ func (p *PriorityQueue) NominatedPodsForNode(nodeName string) []*v1.Pod {
 func (p *PriorityQueue) PendingPods() []*v1.Pod {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
-	result := []*v1.Pod{}
+	var result []*v1.Pod
 	for _, pInfo := range p.activeQ.List() {
 		result = append(result, pInfo.(*framework.QueuedPodInfo).Pod)
 	}