fix image manager Start() function return

realImageGCManager's Start()  function will always return nil,we do not need the err return value,drop it.

pkg/kubelet/kubelet.go

@@ -1177,9 +1177,7 @@ func (kl *Kubelet) initializeModules() error {
 	}
 
 	// Step 4: Start the image manager.
-	if err := kl.imageManager.Start(); err != nil {
-		return fmt.Errorf("Failed to start ImageManager, images may not be garbage collected: %v", err)
-	}
+	kl.imageManager.Start()
 
 	// Step 5: Start container manager.
 	node, err := kl.getNodeAnyWay()