BUG: Bug in Timestamp-Timestamp not returning a Timedelta type (GH8865)

closes #8865 
```
(Pdb) p dt_tz
datetime.datetime(2013, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>)
(Pdb) p dt
datetime.datetime(2013, 1, 1, 0, 0)
(Pdb) p dt_tz - dt
*** TypeError: TypeError("can't subtract offset-naive and offset-aware datetimes",)
```

``datetime-datetime`` has this as a ``TypeError`` (that's why I changed it, originally I had it as a ValueError as well)