Replace drupal_container() with Drupal::keyValue() in the update module

#2 looks good. I didn't find any more uses of drupal_container() in the update module.

I think those should be Drupal::keyValue() instead.

I am attaching a patch altered as per @webchick's recommendations.

I am a little confused about this, though. I read here that it it is preferred to use the service container to instantiate objects. As per the following block:

  // The preferred way: dependency injected code.
  function hook_do_stuff() {
    // Move the actual implementation to a class and instantiate it.
    $instance = new StuffDoingClass(Drupal::lock());
    $instance->doStuff();

    // Or, even better, rely on the service container to avoid hard coding a
    // specific interface implementation, so that the actual logic can be
    // swapped. This might not always make sense, but in general it is a good
    // practice.
    Drupal::service('stuff.doing')->doStuff();
  }

Calling Drupal::keyValue() seems to me to be a direct implementation detail. Of course, I checked the implementation and see that it just calls the container. I am not sure which is the better method. However, like I said, I am using Drupal::keyValue() as per @webchick's recommendation, but I would like someone to throw some light on this.

Sorry about the empty patch. Here is the correct one.

Seems good for me.

Committed fc35679 and pushed to 8.x. Thanks!

@kgoel the move to closed(fixed) will happen automatically after 2 weeks without further comments.