Remove ``item`` for the :class:`zset` it it exists.
        If found it returns the score of the item removed.

def remove(self, item):
        '''Remove ``item`` for the :class:`zset` it it exists.
        If found it returns the score of the item removed.
        '''
        score = self._dict.pop(item, None)
        if score is not None:
            index = self._sl.rank(score)
            assert index >= 0, 'could not find start range'
            for i, v in enumerate(self._sl.range(index)):
                if v == item:
                    assert self._sl.remove_range(index + i, index+i + 1) == 1
                    return score
            assert False, 'could not find element'