Uninstalls handlers for events.

        :param session: Unique logical identifier to a session.
        :param event_type: Logical event identifier.
        :param handler: Interpreted as a valid reference to a handler to be uninstalled by a client application.
        :param user_handle: The user handle (ctypes object or None) returned by install_visa_handler.

def uninstall_visa_handler(self, session, event_type, handler, user_handle=None):
        """Uninstalls handlers for events.

        :param session: Unique logical identifier to a session.
        :param event_type: Logical event identifier.
        :param handler: Interpreted as a valid reference to a handler to be uninstalled by a client application.
        :param user_handle: The user handle (ctypes object or None) returned by install_visa_handler.
        """
        for ndx, element in enumerate(self.handlers[session]):
            if element[0] is handler and element[1] is user_handle and element[4] == event_type:
                del self.handlers[session][ndx]
                break
        else:
            raise errors.UnknownHandler(event_type, handler, user_handle)
        self.uninstall_handler(session, event_type,  element[2], user_handle)