## 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 = {
            "result": [
                {"days": ["2020-11-01 05:20:00", "2020-11-01 10:22:00", "2020-11-01 10:25:00"], "data": [0.0, 0.0, 0.0]}
            ]
        }
        filter = Filter(
            data={
                "date_to": "2020-11-01 10:26:00",
                "events": [{"id": "sign up", "name": "sign up"}],
                "interval": "hour",
            },
            team=self.team,
        )
        cache_key = generate_cache_key(f"{filter.toJSON()}_{self.team.pk}")
        cache.set(cache_key, fake_cached, settings.CACHED_RESULTS_TTL)
        res = Trends().get_cached_result(filter, self.team)
        self.assertIsNotNone(res)
        filter = Filter(
            data={
                "date_to": "2020-11-02 05:26:00",
                "events": [{"id": "sign up", "name": "sign up"}],
                "interval": "hour",
            },
            team=self.team,
        )
        res = Trends().get_cached_result(filter, self.team)
        self.assertIsNone(res)
    def test_get_cached_result_day(self):