code: func (h *RegistrationHandler) DeRegisterPlugin(pluginName string) {
  	klog.V(4).Info(log("registrationHandler.DeRegisterPlugin request for plugin %s", pluginName))
  	if err := unregisterDriver(pluginName); err != nil {
  		klog.Error(log("registrationHandler.DeRegisterPlugin failed: %v", err))
  	}
  }
docs: // DeRegisterPlugin is called when a plugin removed its socket, signaling
  // it is no longer available