Prevent deleting translations

Test steps for the MR:

1. drush si -y
2. drush en -y content_translation trash
3. Go to /admin/config/regional/language and add Spanish as a new language
4. Go to /admin/config/regional/content-language and enable translation for Article nodes
5. Add a new Article
6. Add a Spanish translation
7. Go to /es/node/1/delete, and ensure you can't submit the form. There should be a message saying "Moving translations to the trash bin is currently not supported. Unpublish the translation instead.".

Posted an issue in the MR.

Merged into 3.x, thanks!

I had a look at the MR and did some testing and this looks good to me as well, thanks!