[IMP] ir_qweb: remove the option 'only_date' introducted in cefc9ad8e3e3b0a14804da6c40bfd71e16d4175a. Now we can use widget='date' to do the same thing. That keeps the same behaviour that in the backend.

    <span t-field=model.datetime_field t-field-options="{'widget': 'date'}"/>