## 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
"1-Nov-2020 13:00",
                        "1-Nov-2020 14:00",
                        "1-Nov-2020 15:00",
                        "1-Nov-2020 16:00",
                        "1-Nov-2020 17:00",
                        "1-Nov-2020 18:00",
                        "1-Nov-2020 19:00",
                        "1-Nov-2020 20:00",
                        "1-Nov-2020 21:00",
                        "1-Nov-2020 22:00",
                        "1-Nov-2020 23:00",
                    ],
                    "days": [
                        "2020-11-01 12:00:00",
                        "2020-11-01 13:00:00",
                        "2020-11-01 14:00:00",
                        "2020-11-01 15:00:00",
                        "2020-11-01 16:00:00",
                        "2020-11-01 17:00:00",
                        "2020-11-01 18:00:00",
                        "2020-11-01 19:00:00",
                        "2020-11-01 20:00:00",
                        "2020-11-01 21:00:00",
                        "2020-11-01 22:00:00",
                        "2020-11-01 23:00:00",
                    ],
                }
            ],
        )
    def test_day_interval(self):