bug: Remove timezone info from shiny.datetime input handler

[schloerke]

Followup to #1142 and #1143
Fixes #1144

>>> datetime.fromtimestamp(1, tz = timezone.utc)
datetime.datetime(1970, 1, 1, 0, 0, 1, tzinfo=datetime.timezone.utc)
>>> str(datetime.fromtimestamp(1, tz = timezone.utc))
'1970-01-01 00:00:01+00:00'

>>> pr = datetime.fromtimestamp(1, tz = timezone.utc).replace(tzinfo=None)
>>> pr
datetime.datetime(1970, 1, 1, 0, 0, 1)
>>> before = datetime.utcfromtimestamp(1)
datetime.datetime(1970, 1, 1, 0, 0, 1)

>>> str(pr)
'1970-01-01 00:00:01'
>>> before = datetime.utcfromtimestamp(1)
>>> str(before)
'1970-01-01 00:00:01'