## 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
"2020-11-05 08:25:00",
                "2020-11-05 08:25:00",
                "2020-11-10 08:25:00",
            ],
            date_from="-14d",
            query_time="2020-11-14 10:20:00",
            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": 6.0,
                    "data": [0.0, 1.0, 1.0, 0.0, 1.0, 2.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 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",