Revert changes to comparison between Series[datetime64ns] and datetime.date
Revert the changes in https://github.com/pandas-dev/pandas/pull/21361

- [ ]: Remove check in `core/ops.py`
- [ ]: Remove test `pandas/tests/tseries/test_arithmetic.py::TestTimestampSeriesComparison.test_dt64_ser_cmp_date_warning`
- [ ]: Reenable test `pandas/tests/tseries/test_arithmetic.py::TestTimestampSeriesComparison.test_dt64ser_cmp_date_invalid`

Target this for 0.24?

xref https://github.com/pandas-dev/pandas/issues/21152
