There does not appear to be an option to delete a draft, only to archive it.
You can now delete a draft when it is archived.
We should be able to delete the draft. before archiving it, not just delete an archived draft... but the option to either merge, delete, or archive.
We plan on making it possible to delete an archive draft in an important improvement of the editing UX.
@Samy Pessé: What will happen to archived drafts? Will they be deleted eventually like after a certain amount of days?
@Ivan Huang: No deleting an archived draft will be an explicit action (with a confirmation prompt).
You can have as much archived drafts as you want.