Don't store default edition in the dataase

bookwyrm/views/helpers.py

@@ -123,7 +123,7 @@ def get_edition(book_id):
     """look up a book in the db and return an edition"""
     book = models.Book.objects.select_subclasses().get(id=book_id)
     if isinstance(book, models.Work):
-        book = book.get_default_edition()
+        book = book.default_edition
     return book