## 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_person(team_id=self.team.pk, properties={"email": "foo@example.com", "bar": "aa"}, distinct_ids=["d1"])
        _create_person(team_id=self.team.pk, properties={"email": "bar@example.com", "bar": "bb"}, distinct_ids=["d2"])
        _create_person(team_id=self.team.pk, properties={"email": "efg@example.com", "bar": "ab"}, distinct_ids=["d3"])
        _create_person(team_id=self.team.pk, properties={"bar": "aa"}, distinct_ids=["d4"])
        with freeze_time("2020-01-02 16:34:34"):
            _create_event(team=self.team, event="$pageview", distinct_id="d1")
            _create_event(team=self.team, event="$pageview", distinct_id="d2")
            _create_event(team=self.team, event="$pageview", distinct_id="d3")
            _create_event(team=self.team, event="$pageview", distinct_id="d4")
        event_filtering_action = Action.objects.create(team=self.team, name="$pageview from non-internal")
        ActionStep.objects.create(
            action=event_filtering_action,
            event="$pageview",
            properties=[{"key": "bar", "type": "person", "value": "a", "operator": "icontains"}],
        )
        with freeze_time("2020-01-04T13:01:01Z"):
            response = Trends().run(Filter({"actions": [{"id": event_filtering_action.id}]}), self.team)
        self.assertEqual(len(response), 1)
        self.assertEqual(response[0]["count"], 3)
        with freeze_time("2020-01-04T13:01:01Z"):
            response_with_email_filter = Trends().run(
                Filter(
                    {
                        "actions": [{"id": event_filtering_action.id}],