Remove sync provider support

This removes the legacy sync provider interface. All new providers
are expected to implement the async NotifyPods interface.

The legacy sync provider interface creates complexities around
how the deletion flow works, and the mixed sync and async APIs
block us from evolving functionality.

This collapses in the NotifyPods interface into the PodLifecycleHandler
interface.

node/queue.go

@@ -16,12 +16,10 @@ package node
 
 import (
 	"context"
-	"time"
 
 	pkgerrors "github.com/pkg/errors"
 	"github.com/virtual-kubelet/virtual-kubelet/log"
 	"github.com/virtual-kubelet/virtual-kubelet/trace"
-	corev1 "k8s.io/api/core/v1"
 	"k8s.io/client-go/util/workqueue"
 )
 
@@ -105,40 +103,3 @@ func (pc *PodController) processPodStatusUpdate(ctx context.Context, workerID st
 
 	return handleQueueItem(ctx, q, pc.podStatusHandler)
 }
-
-// providerSyncLoop synchronizes pod states from the provider back to kubernetes
-// Deprecated: This is only used when the provider does not support async updates
-// Providers should implement async update support, even if it just means copying
-// something like this in.
-func (pc *PodController) providerSyncLoop(ctx context.Context, q workqueue.RateLimitingInterface) {
-	const sleepTime = 5 * time.Second
-
-	t := time.NewTimer(sleepTime)
-	defer t.Stop()
-
-	for {
-		select {
-		case <-ctx.Done():
-			return
-		case <-t.C:
-			t.Stop()
-
-			ctx, span := trace.StartSpan(ctx, "syncActualState")
-			pc.fetchPodStatusesFromProvider(ctx, q)
-			span.End()
-
-			// restart the timer
-			t.Reset(sleepTime)
-		}
-	}
-}
-
-func (pc *PodController) runSyncFromProvider(ctx context.Context, q workqueue.RateLimitingInterface) {
-	if pn, ok := pc.provider.(PodNotifier); ok {
-		pn.NotifyPods(ctx, func(pod *corev1.Pod) {
-			pc.enqueuePodStatusUpdate(ctx, q, pod.DeepCopy())
-		})
-	} else {
-		go pc.providerSyncLoop(ctx, q)
-	}
-}