## 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()
        with freeze_time("2020-01-04T13:00:01Z"):
            response = Trends().run(
                Filter(
                    data={
                        "date_from": "-7d",
                        "events": [
                            {"id": "sign up", "properties": [{"key": "$some_property", "value": "value"}]},
                            {"id": "sign up", "properties": [{"key": "$some_property", "value": "other_value"}]},
                        ],
                    }
                ),
                self.team,
            )
        self.assertEqual(response[0]["labels"][4], "1-Jan-2020")
        self.assertEqual(response[0]["data"][4], 1)
        self.assertEqual(response[0]["count"], 1)
        self.assertEqual(response[1]["labels"][5], "2-Jan-2020")
        self.assertEqual(response[1]["data"][5], 1)
        self.assertEqual(response[1]["count"], 1)
    def _create_multiple_people(self):