## Bug description

When calculating Trends results with an aggregated (e.g. single output, like big number) display type, WAU/MAU don't work. This is because we have an `ACTIVE_USERS_SQL` query for time series display types, but we don't have a version of this for aggregated display types. (See ZEN-1043.)

## How to reproduce

1. Create an insight with a single WAU or MAU series.
2. Switch display type to "Number".
3. Open the "Debug ClickHouse queries" modal from the command palette.
4. See `COUNT(*)` instead of `COUNT(DISTINCT person_id)`.

#### *Thank you* for your bug report – we love squashing them!

posthog/queries/test/test_trends.py
self._create_active_users_events()
        data = {
            "date_from": "2020-01-09T06:00:00Z",
            "date_to": "2020-01-09T17:00:00Z",
            "interval": "hour",
            "events": [{"id": "$pageview", "type": "events", "order": 0, "math": "weekly_active"}],
        }
        filter = Filter(data=data)
        result = Trends().run(filter, self.team)
        self.assertEqual(
            result[0]["days"],
            [
                "2020-01-09 06:00:00",
                "2020-01-09 07:00:00",
                "2020-01-09 08:00:00",
                "2020-01-09 09:00:00",
                "2020-01-09 10:00:00",
                "2020-01-09 11:00:00",
                "2020-01-09 12:00:00",
                "2020-01-09 13:00:00",
                "2020-01-09 14:00:00",
                "2020-01-09 15:00:00",
                "2020-01-09 16:00:00",