Timezone value is not being saved

/**
* Plugin implementation of the 'daterange_timezone' widget.
*
* @FieldWidget(
* id = "daterange_timezone",
* label = @Translation("Date and time range (with timezone)"),
* field_types = {
* "daterange",
* "daterange_timezone"
* }
* )
*/

re: usecase -- perhaps this module should NOT be allow on daterange?

True, widget does not save selected with core field type daterange, but only with module provided daterange_timezone

removes `daterange` from field widget, per comment #5