Remove the pairs identified by the given indices into _pairs.
        
        Removes the pair, and updates the _key_ids mapping to be accurate.
        Removing the ids from the _key_ids is your own responsibility.
        
        Params:
            ids_to_remove -- The indices to remove. MUST be sorted.

def _remove_pairs(self, ids_to_remove):
        """Remove the pairs identified by the given indices into _pairs.
        
        Removes the pair, and updates the _key_ids mapping to be accurate.
        Removing the ids from the _key_ids is your own responsibility.
        
        Params:
            ids_to_remove -- The indices to remove. MUST be sorted.
        
        """
        # Remove them.
        for i in reversed(ids_to_remove):
            del self._pairs[i]
        
        # We use the bisect to tell us how many spots the given index is
        # shifting up in the list.
        for ids in self._key_ids.itervalues():
            for i, id in enumerate(ids):
                ids[i] -= bisect(ids_to_remove, id)