## 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, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 0.0],
                    "labels": [
                        "31-Oct-2020",
                        "1-Nov-2020",
                        "2-Nov-2020",
                        "3-Nov-2020",
                        "4-Nov-2020",
                        "5-Nov-2020",
                        "6-Nov-2020",
                        "7-Nov-2020",
                    ],
                    "days": [
                        "2020-10-31",
                        "2020-11-01",
                        "2020-11-02",
                        "2020-11-03",
                        "2020-11-04",
                        "2020-11-05",
                        "2020-11-06",
                        "2020-11-07",
                    ],
                }
            ],
        )
    def test_last14days_timerange(self):
        self._test_events_with_dates(
            dates=[
                "2020-11-01 05:20:00",
                "2020-11-02 10:22:00",
                "2020-11-04 10:25:00",