code: def remove_outdated(self, when=0):
          
          for iss in list(self.owners()):
              _kbl = []
              for kb in self.issuer_keys[iss]:
                  kb.remove_outdated(self.remove_after, when=when)
                  if len(kb):
                      _kbl.append(kb)
              if _kbl:
                  self.issuer_keys[iss] = _kbl
              else:
                  del self.issuer_keys[iss]
docs: Goes through the complete list of issuers and for each of them removes
          outdated keys.
          Outdated keys are keys that has been marked as inactive at a time that
          is longer ago then some set number of seconds (when). If when=0 the
          the base time is set to now.
          The number of seconds a carried in the remove_after parameter in the
          key jar.
  
          :param when: To facilitate testing