## 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
distinct_id="blabla",
            properties={"$session_id": 4},
            timestamp="2020-01-02 00:06:45",
        )
        
        with freeze_time("2020-01-04T13:00:01Z"):
            daily_response = Trends().run(
                Filter(
                    data={
                        "display": TRENDS_TABLE,
                        "interval": "week",
                        "events": [{"id": "sign up", "math": "median", "math_property": "$session_duration"}],
                    }
                ),
                self.team,
            )
        with freeze_time("2020-01-04T13:00:01Z"):
            weekly_response = Trends().run(
                Filter(
                    data={
                        "display": TRENDS_TABLE,
                        "interval": "day",
                        "events": [{"id": "sign up", "math": "median", "math_property": "$session_duration"}],
                    }
                ),
                self.team,
            )
        self.assertEqual(daily_response[0]["aggregated_value"], 7.5)
        self.assertEqual(daily_response[0]["aggregated_value"], weekly_response[0]["aggregated_value"])
    def test_unique_session_with_session_breakdown(self):