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/templates/snippets/authors.html

@@ -1 +1 @@
-<a href="/author/{{ book.authors.first.id }}" class="author">{{ book.authors.first.display_name }}</a>
+<a href="/author/{{ book.authors.first.id }}" class="author">{{ book.authors.first.name }}</a>

bookwyrm/templates/snippets/shelf.html

@@ -43,7 +43,7 @@
         <a href="/book/{{ book.id }}">{{ book.title }}</a>
     </td>
     <td>
-        {{ book.authors.first.display_name }}
+        {{ book.authors.first.name }}
     </td>
     <td>
         {% if book.first_published_date %}{{ book.first_published_date }}{% endif %}