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/migrations/0022_auto_20201212_1744.py

@@ -0,0 +1,30 @@
+# Generated by Django 3.0.7 on 2020-12-12 17:44
+
+from django.db import migrations
+
+
+def set_author_name(app_registry, schema_editor):
+    db_alias = schema_editor.connection.alias
+    authors = app_registry.get_model('bookwyrm', 'Author')
+    for author in authors.objects.using(db_alias):
+        if not author.name:
+            author.name = '%s %s' % (author.first_name, author.last_name)
+            author.save()
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('bookwyrm', '0021_merge_20201212_1737'),
+    ]
+
+    operations = [
+        migrations.RunPython(set_author_name),
+        migrations.RemoveField(
+            model_name='author',
+            name='first_name',
+        ),
+        migrations.RemoveField(
+            model_name='author',
+            name='last_name',
+        ),
+    ]