Removes the opinion for the given opinion identifier
        @type opinion_id: string
        @param opinion_id: the opinion identifier to be removed

def remove_this_opinion(self,opinion_id):
        """
        Removes the opinion for the given opinion identifier
        @type opinion_id: string
        @param opinion_id: the opinion identifier to be removed
        """
        for opi in self.get_opinions():
            if opi.get_id() == opinion_id:
                self.node.remove(opi.get_node())
                break