docs: def remove_duplicates(self, configs=None):
          """remove duplicate entries from 4-point configurations. If no
          configurations are provided, then use self.configs. Unique
          configurations are only returned if configs is not None.
  
          Parameters
          ----------
          configs: Nx4 numpy.ndarray, optional
              remove duplicates from these configurations instead from
              self.configs.
  
          Returns
          -------
          configs_unique: Kx4 numpy.ndarray
              unique configurations. Only returned if configs is not None
  
          """
          if configs is None:
              c = self.configs
          else:
              c = configs
          struct = c.view(c.dtype.descr * 4)
          configs_unique = np.unique(struct).view(c.dtype).reshape(-1, 4)
          if configs is None:
              self.configs = configs_unique
          else:
              return configs_unique