Delete current metadata of `symbol`

        Parameters
        ----------
        symbol : `str`
            symbol name to delete

        Returns
        -------
        Deleted metadata

def pop(self, symbol):
        """
        Delete current metadata of `symbol`

        Parameters
        ----------
        symbol : `str`
            symbol name to delete

        Returns
        -------
        Deleted metadata
        """
        last_metadata = self.find_one({'symbol': symbol}, sort=[('start_time', pymongo.DESCENDING)])
        if last_metadata is None:
            raise NoDataFoundException('No metadata found for symbol {}'.format(symbol))

        self.find_one_and_delete({'symbol': symbol}, sort=[('start_time', pymongo.DESCENDING)])
        mongo_retry(self.find_one_and_update)({'symbol': symbol}, {'$unset': {'end_time': ''}},
                                              sort=[('start_time', pymongo.DESCENDING)])

        return last_metadata