Remove entity from the MatchBox.

        :param object entity:

def remove(self, entity):
        """
        Remove entity from the MatchBox.

        :param object entity:
        """
        empty_traits = set()
        self.mismatch_unknown.discard(entity)
        for trait, entities in self.index.items():
            entities.discard(entity)
            if not entities:
                empty_traits.add(trait)

        for empty_trait in empty_traits:
            del self.index[empty_trait]