## 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_events(use_time=True)
        with freeze_time("2020-01-02T20:17:00Z"):
            response = Trends().run(
                Filter(
                    data={
                        "compare": "true",
                        "date_from": "dStart",
                        "interval": "hour",
                        "events": [{"id": "sign up"}],
                    }
                ),
                self.team,
            )
        self.assertEqual(
            response[0]["days"],
            [
                "2020-01-02 00:00:00",
                "2020-01-02 01:00:00",
                "2020-01-02 02:00:00",
                "2020-01-02 03:00:00",
                "2020-01-02 04:00:00",
                "2020-01-02 05:00:00",
                "2020-01-02 06:00:00",
                "2020-01-02 07:00:00",
                "2020-01-02 08:00:00",
                "2020-01-02 09:00:00",
                "2020-01-02 10:00:00",
                "2020-01-02 11:00:00",