## 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
set_instance_setting("STRICT_CACHING_TEAMS", "all")
        fake_cached = {
            "sign up - Chrome_0": {
                "label": "sign up - Chrome",
                "days": ["2020-01-02", "2020-01-03", "2020-01-04"],
                "data": [23.0, 15.0, 1.0],
            },
            "sign up - Safari_0": {
                "label": "sign up - Safari",
                "days": ["2020-01-02", "2020-01-03", "2020-01-04"],
                "data": [12.0, 11.0, 8.0],
            },
        }
        filter = Filter(
            data={"date_from": "2020-01-02", "date_to": "2020-01-04", "events": [{"id": "sign up", "name": "sign up"}]},
            team=self.team,
        )
        result = [
            {"label": "sign up - Chrome", "data": [15.0, 12.0]},
            {"label": "sign up - Safari", "data": [15.0, 9.0]},
        ]
        merged_result, _ = Trends().merge_results(result, fake_cached, 0, filter, self.team)
        self.assertEqual(merged_result[0]["data"], [23.0, 15.0, 12.0])
        self.assertEqual(merged_result[1]["data"], [12.0, 11.0, 9.0])