## 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
Filter(
                data={
                    "date_from": "2020-01-01 00:00:00",
                    "date_to": "2020-07-01 00:00:00",
                    "breakdown": "email",
                    "breakdown_type": "person",
                    "events": [{"id": "sign up", "name": "sign up", "type": "events", "order": 0}],
                    "properties": {
                        "type": "AND",
                        "values": [
                            {
                                "type": "OR",
                                "values": [
                                    {
                                        "key": "email",
                                        "value": "@posthog.com",
                                        "operator": "not_icontains",
                                        "type": "person",
                                    },
                                    {"key": "key", "value": "val"},
                                ],
                            },
                            {
                                "type": "OR",
                                "values": [
                                    {"key": "$os", "value": "android", "operator": "exact", "type": "person"},
                                    {"key": "$browser", "value": "safari", "operator": "exact", "type": "person"},
                                ],
                            },
                        ],