## 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_groups()
        _create_event(
            event="sign up",
            distinct_id="person1",
            team=self.team,
            properties={"key": "oh", "$group_0": "org:7", "$group_1": "company:10"},
            timestamp="2020-01-02T12:00:00Z",
        )
        _create_event(
            event="sign up",
            distinct_id="person1",
            team=self.team,
            properties={"key": "uh", "$group_0": "org:5"},
            timestamp="2020-01-02T12:00:01Z",
        )
        _create_event(
            event="sign up",
            distinct_id="person1",
            team=self.team,
            properties={"key": "uh", "$group_0": "org:6"},
            timestamp="2020-01-02T12:00:02Z",
        )
        response = Trends().run(
            Filter(
                data={