I believe the filter works the same way that the regular filter UI works in dashboard. For example, if you select Alabama from a filter drop-down, you have to use the filter drop-down to clear the filter. If you want to create an external UI element to clear the filter, you should be able to use the clearFilterAsync method. E.g.
activeSheet.getWorksheets().get('Tableau Test 1').clearFilterAsync('State');
Hope that helps!