Do not convert series when looking at sub-daily frequencies.

Fixes #8772 by not converting values from UTC to local timezone when trying to infer sub-daily frequencies.  Across a DST transition this will result in a non-unique deltas and an inferred frequency of None.
Maybe add this:

```python
        index = date_range("2013-11-03", periods=5, freq="3H").tz_localize("America/Chicago")
        self.assertIsNone(index.inferred_freq)
```