docs: def remove_token(self, act):
          """
          Remove a token from the proactor.
          If removal succeeds (the token is in the proactor) return True.
          """
          if act in self.tokens:
              self.unregister_fd(act)
              del self.tokens[act]
              return True
          else:
              import warnings
              warnings.warn("%s isn't a registered token." % act)