## 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
"data": [0.0, 3.0, 2.0, 0.0, 1.0, 0.0],
                    "labels": [
                        "25-Oct-2020",
                        "1-Nov-2020",
                        "8-Nov-2020",
                        "15-Nov-2020",
                        "22-Nov-2020",
                        "29-Nov-2020",
                    ],
                    "days": ["2020-10-25", "2020-11-01", "2020-11-08", "2020-11-15", "2020-11-22", "2020-11-29"],
                }
            ],
        )
    def test_last90days_timerange(self):
        self._test_events_with_dates(
            dates=[
                "2020-09-01 05:20:00",
                "2020-10-05 05:20:00",
                "2020-10-20 05:20:00",
                "2020-11-01 05:20:00",
                "2020-11-11 10:22:00",
                "2020-11-24 10:25:00",
                "2020-11-05 08:25:00",
                "2020-11-05 08:25:00",
                "2020-11-10 08:25:00",
            ],
            date_from="-90d",
            interval="month",
            query_time="2020-11-30 10:20:00",
            result=[