## 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
person1 = _create_person(team_id=self.team.pk, distinct_ids=["person1"], properties={"name": "person1"})
        person2 = _create_person(team_id=self.team.pk, distinct_ids=["person2"], properties={"name": "person2"})
        person3 = _create_person(team_id=self.team.pk, distinct_ids=["person3"], properties={"name": "person3"})
        person4 = _create_person(team_id=self.team.pk, distinct_ids=["person4"], properties={"name": "person4"})
        journey = {
            "person1": [
                {
                    "event": "watched movie",
                    "timestamp": datetime(2020, 1, 1, 12),
                    "properties": {"order": "1", "name": "1"},
                }
            ],
            "person2": [
                {
                    "event": "watched movie",
                    "timestamp": datetime(2020, 1, 1, 12),
                    "properties": {"order": "1", "name": "2"},
                },
                {
                    "event": "watched movie",
                    "timestamp": datetime(2020, 1, 2, 12),
                    "properties": {"order": "2", "name": "2"},
                },
                {
                    "event": "watched movie",
                    "timestamp": datetime(2020, 1, 2, 12),
                    "properties": {"order": "2", "name": "2"},
                },
            ],