Fix the oauth toolkit checksum migration

aleksis/core/migrations/0070_oauth_token_checksum.py

@@ -26,7 +26,7 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='oauthaccesstoken',
             name='token_checksum',
-            field=oauth2_provider.models.TokenChecksumField(db_index=True, default='', max_length=64, unique=True, blank=True),
+            field=oauth2_provider.models.TokenChecksumField(default='', max_length=64, blank=True),
             preserve_default=False,
         ),
         migrations.RunPython(forwards_func, migrations.RunPython.noop),