Clean up content_translation_entity_presave()

This came up before I believe, like in issues that tried to add proper methods for $entity->original and got stalled.

The thing is that it obviously doesn't ever go in there, as this would be a fatal error then. And $entity->original really should always be set. This might be some left-over cruft from 7.x when people did crazy things to just save single fields and so on.

So I'd suggest to just drop the whole part completely, *maybe* add a && $entity->original in the initial condition but I don't think we really bother with that in other hooks.

I will work on this in DrupalGlobalSprintWeekenddelhi2019

Here is the patch.

This will not work as ->getStorage() requires string (entity type) as argument and in this case it will object.

What I understand from the #3 is that we just need to add the condition && $entity->original at top like this -
if ($entity instanceof ContentEntityInterface && $entity->isTranslatable() && !$entity->isNew()) && $entity->original) {}

Here is the updated comment.

Doesn't make a difference as it goes through __get(), but we should get back to the issue about adding methods for that anyway.

Committed 4a43a3b and pushed to 8.7.x. Thanks!