## 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
self._test_events_with_dates(
            dates=["2020-07-10", "2020-07-30", "2020-10-18"],
            interval="month",
            date_from="2020-6-01",
            date_to="2020-11-24",
            result=[
                {
                    "action": {
                        "id": "event_name",
                        "type": "events",
                        "order": None,
                        "name": "event_name",
                        "custom_name": None,
                        "math": None,
                        "math_property": None,
                        "math_group_type_index": None,
                        "properties": [],
                    },
                    "label": "event_name",
                    "count": 3.0,
                    "data": [0.0, 2.0, 0.0, 0.0, 1.0, 0.0],
                    "labels": ["1-Jun-2020", "1-Jul-2020", "1-Aug-2020", "1-Sep-2020", "1-Oct-2020", "1-Nov-2020"],
                    "days": ["2020-06-01", "2020-07-01", "2020-08-01", "2020-09-01", "2020-10-01", "2020-11-01"],
                }
            ],
        )
    def test_interval_rounding(self):