Use name field only for author name

It feels janky to remove a more granular name designation, but all these
first/last name fields were algorithmically populated by a dubious
process of splitting the name by a space character. If it makes sense to
have first/last name fields, it should be re-added with some
consideration.

bookwyrm/tests/activitypub/test_author.py

@@ -12,8 +12,6 @@ class Author(TestCase):
         )
         self.author = models.Author.objects.create(
             name='Author fullname',
-            first_name='Auth',
-            last_name='Or',
             aliases=['One', 'Two'],
             bio='bio bio bio',
         )