Merge pull request #53564 from supereagle/remove-network-plugin-dir-flag

Automatic merge from submit-queue (batch tested with PRs 53743, 53564). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubelet: remove the --network-plugin-dir flag

**What this PR does / why we need it**:
This flag has been replaced with `--cni-bin-dir`,  and has been deprecated in Kubernetes 1.7.
It is safe to remove in Kubernetes 1.9 according to the deprecation policy.

**Which issue this PR fixes**: fixes #46410

**Special notes for your reviewer**:
/assign @mtaufen @freehan @dchen1107

**Release note**:
```release-note
Remove the --network-plugin-dir flag.
```

cmd/kubelet/app/server.go

@@ -164,7 +164,7 @@ func UnsecuredDependencies(s *options.KubeletServer) (*kubelet.Dependencies, err
 		ExternalKubeClient:  nil,
 		EventClient:         nil,
 		Mounter:             mounter,
-		NetworkPlugins:      ProbeNetworkPlugins(s.NetworkPluginDir, s.CNIConfDir, s.CNIBinDir),
+		NetworkPlugins:      ProbeNetworkPlugins(s.CNIConfDir, s.CNIBinDir),
 		OOMAdjuster:         oom.NewOOMAdjuster(),
 		OSInterface:         kubecontainer.RealOS{},
 		Writer:              writer,
@@ -898,9 +898,6 @@ func RunDockershim(f *options.KubeletFlags, c *kubeletconfiginternal.KubeletConf
 
 	// Initialize network plugin settings.
 	binDir := r.CNIBinDir
-	if binDir == "" {
-		binDir = r.NetworkPluginDir
-	}
 	nh := &kubelet.NoOpLegacyHost{}
 	pluginSettings := dockershim.NetworkPluginSettings{
 		HairpinMode:       kubeletconfiginternal.HairpinMode(c.HairpinMode),