remove removed table reference

https://bugzilla.mozilla.org/show_bug.cgi?id=951703

This fixes the `DatabaseError` from `unconfirmed` in [mat's gist](https://gist.github.com/diox/502a20a58d156e5d375a).

The join was removed in 7f4304d78b5372d7e8c349fb622471343d2446b0 so the query failed on the `WHERE`.