## 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
# CH 
        # Wh
        # On
        # Th
        # 1. 
        # 2. 
        with freeze_time("2020-01-04T13:01:01Z"):
            Trends().run(
                Filter(
                    data={
                        "date_from": "-14d",
                        "events": [{"id": "watched movie", "name": "watched movie", "type": "events", "order": 0}],
                        "properties": [
                            {"key": "email", "type": "event", "value": "posthog.com", "operator": "not_icontains"},
                            {"key": "name", "type": "event", "value": "posthog.com", "operator": "not_icontains"},
                            {"key": "name", "type": "person", "value": "posthog.com", "operator": "not_icontains"},
                        ],
                    }
                ),
                self.team,
            )
    def test_trends__per_user_average(self):