Fix TypeError bug in RDATE all day event handling

[allenporter]

Fix bug in RDATE all day event handling:

tests/test_timeline.py:916: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../ical/ical/iter.py:234: in overlapping
    for item in self._iterable:
../ical/ical/iter.py:143: in __next__
    self._make_heap()
../ical/ical/iter.py:133: in _make_heap
    next_item = next(iterator)
../ical/ical/iter.py:113: in __iter__
    for dtvalue in self._recur:
gcal_sync/timeline.py:106: in __iter__
    for value in self._func:
gcal_sync/timeline.py:92: in __iter__
    for value in self._dt_iter:
../ical/ical/iter.py:113: in __iter__
    for dtvalue in self._recur:
venv/lib/python3.9/site-packages/dateutil/rrule.py:1396: in _iter
    heapq.heapify(rlist)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <dateutil.rrule.rruleset._genitem object at 0x7f484cc22b50>
other = <dateutil.rrule.rruleset._genitem object at 0x7f484cc221c0>

    def __lt__(self, other):
>       return self.dt < other.dt
E       TypeError: can't compare datetime.datetime to datetime.date

venv/lib/python3.9/site-packages/dateutil/rrule.py:1338: TypeError

The approach is to simplify the date vs datetime workaround that already exists, due to limitations in dateutil.rrule when used in a dateutil.ruleset.