kubelet: do not force update the runtime cache

Pod workers don't rely on the old runtime cache to sync pods anymore. There is
no need to force update the cache on every container event.

pkg/kubelet/kubelet.go

@@ -2598,12 +2598,6 @@ func (kl *Kubelet) syncLoopIteration(configCh <-chan kubetypes.PodUpdate, handle
 			break
 		}
 		glog.V(2).Infof("SyncLoop (PLEG): %q, event: %#v", format.Pod(pod), e)
-		// Force the container runtime cache to update.
-		if err := kl.runtimeCache.ForceUpdateIfOlder(kl.clock.Now()); err != nil {
-			glog.Errorf("SyncLoop: unable to update runtime cache")
-			// TODO (yujuhong): should we delay the sync until container
-			// runtime can be updated?
-		}
 		handler.HandlePodSyncs([]*api.Pod{pod})
 	case <-syncCh:
 		// Sync pods waiting for sync