## 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
_create_event(
            team=self.team,
            event="watched movie",
            distinct_id="person2",
            timestamp="2020-01-02T12:00:00Z",
            properties={"fake_prop": "value_2"},
        )
        _create_event(
            team=self.team,
            event="watched movie",
            distinct_id="person3",
            timestamp="2020-01-01T12:00:00Z",
            properties={"fake_prop": "value_1"},
        )
        _create_person(team_id=self.team.pk, distinct_ids=["person4"], immediate=True)
        _create_event(
            team=self.team,
            event="watched movie",
            distinct_id="person4",
            timestamp="2020-01-05T12:00:00Z",
            properties={"fake_prop": "value_1"},
        )
        with freeze_time("2020-01-04T13:01:01Z"):
            data = {
                "date_from": "-14d",
                "breakdown": "fake_prop",
                "breakdown_type": "event",
                "display": "ActionsPie",
                "events": [
                    {"id": "watched movie", "name": "watched movie", "type": "events", "order": 0, "math": "dau"}