Make the foreig key from last login table be ON DELETE CASCADE

Since this one is not managed inside Django, it doesn't know what to do
with it when deleting, so just make postgres handle it.

pgweb/account/migrations/0004_cauth_last_login.py

@@ -13,7 +13,7 @@ class Migration(migrations.Migration):
 
     operations = [
         migrations.RunSQL("""CREATE TABLE account_communityauthlastlogin (
-   user_id int NOT NULL REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED,
+   user_id int NOT NULL REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED ON DELETE CASCADE,
    site_id int NOT NULL REFERENCES account_communityauthsite (id) ON DELETE CASCADE DEFERRABLE INITIALLY DEFERRED,
    lastlogin timestamptz NOT NULL,
    logincount bigint NOT NULL,