## 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
"2-Jan-2020",
                "3-Jan-2020",
                "4-Jan-2020",
                "5-Jan-2020",
            ],
        )
        #  
        with freeze_time("2020-01-05T13:01:01Z"):
            response = Trends().run(
                Filter(
                    data={
                        "date_from": "-7d",
                        "breakdown": "$os",
                        "events": [{"id": "sign up", "name": "sign up", "math": "dau"}],
                    },
                    team=self.team,
                ),
                self.team,
            )
            self.assertEqual(response[0]["data"], [0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 0.0, 0.0])
        # C
        response = Trends().run(
            Filter(
                data={
                    "date_from": "2020-01-03",
                    "date_to": "2020-01-03 23:59:59",
                    "interval": "hour",
                    "events": [{"id": "sign up", "name": "sign up"}],
                },
                team=self.team,