Remove a widget from the list.

        :param widget: Object inheriting :class:`~.widgets.base.BaseElement`

def remove_child(self, widget):
        """
        Remove a widget from the list.

        :param widget: Object inheriting :class:`~.widgets.base.BaseElement`
        """
        raw = list(filter(lambda x: x[0] == widget, self._items))
        if raw:
            itm, wrapped = raw[0]
            self._items.remove(raw[0])
            super(List, self).remove_child(wrapped)
        else:
            raise ValueError("Child not in list.")