## 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)`.

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posthog/queries/test/test_trends.py
with freeze_time("2020-01-12T09:01:01Z"):
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$current_url": "first url", "$browser": "Firefox", "$os": "Mac"},
            )
        with freeze_time("2020-01-22T01:01:01Z"):
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$current_url": "second url", "$browser": "Firefox", "$os": "Mac"},
            )
        #  
        with freeze_time("2020-01-26T07:00:00Z"):  # th
            response = Trends().run(
                Filter(
                    data={
                        "date_from": "-14d",
                        "interval": "week",
                        "events": [{"id": "sign up", "name": "sign up"}],
                    },
                    team=self.team,
                ),
                self.team,
            )
        self.assertEqual(response[0]["data"], [1.0, 1.0, 1.0])
        self.assertEqual(response[0]["labels"], ["5-Jan-2020", "12-Jan-2020", "19-Jan-2020"])
    def test_same_day(self):