## 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)`.

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posthog/queries/test/test_trends.py
)
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$some_property": "value", "$math_prop": 1},
            )
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$some_property": "value", "$math_prop": 2},
            )
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$some_property": "value", "$math_prop": 3},
            )
        with freeze_time("2020-01-02 00:06:34"):
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",
                properties={"$some_property": "value", "$math_prop": 4},
            )
            _create_event(
                team=self.team,
                event="sign up",
                distinct_id="blabla",