remove pytz

[deronnax]

To keep it simple, I made it so it imply to drop support for python 3.8, which is already OEL.
Though, I still have this error I am not sure about:

tests/test_xsd_builtins.py:158 (TestDateTime.test_xmlvalue)
'2016-03-04T21:14:42+00:00' != '2016-03-04T21:14:42Z'

Expected :'2016-03-04T21:14:42Z'
Actual   :'2016-03-04T21:14:42+00:00'

<Click to see difference>


self = <tests.test_xsd_builtins.TestDateTime object at 0x1036aa090>

    def test_xmlvalue(self):
        instance = builtins.DateTime()
        value = datetime.datetime(2016, 3, 4, 21, 14, 42)
        assert instance.xmlvalue(value) == "2016-03-04T21:14:42"
    
        value = datetime.datetime(2016, 3, 4, 21, 14, 42, tzinfo=timezone.utc)
>       assert instance.xmlvalue(value) == "2016-03-04T21:14:42Z"
E       AssertionError: assert '2016-03-04T21:14:42+00:00' == '2016-03-04T21:14:42Z'
E         
E         - 2016-03-04T21:14:42Z
E         ?                    ^
E         + 2016-03-04T21:14:42+00:00
E         ?                    ^^^^^^

tests/test_xsd_builtins.py:165: AssertionError

[deronnax]

OK I know why, it's because isodate has a formatting logic that do not recognize python's UTC tzinfo objects: their .dst() method return None, isodate expects a timedelta(0) to consider them UTC.

• either we use isodate's tzinfo everywhere instead of python's one, but that would be a move backward
• either we need to find something so we can get the UTC datetime formatting to have a trailing Z for UTC datetime, because it's not doable out of the box with python standard datetimes.

[JuneStepp]

OK I know why, it's because isodate has a formatting logic that do not recognize python's UTC tzinfo objects: their .dst() method return None, isodate expects a timedelta(0) to consider them UTC.

* either we use isodate's tzinfo everywhere instead of python's one, but that would be a move backward

* either we need to find something so we can get the UTC datetime formatting to have a trailing `Z` for UTC datetime, because it's not doable out of the box with python standard datetimes.

See this commit from my fork: c16230e

[deronnax]

Wow, that's a good work, maybe better than mine. Mind giving your work for #1420 ?