def remove(cls, module_name):
        """
        drop a previously created guard on ``module_name``
        if the module is not guarded, then this is a no-op.
        """
        module_guards = cls._guards.get(module_name, False)
        if module_guards:
            module_guards.pop()
            cls._num_entries -= 1
            if cls._num_entries < 1:
                if cls._num_entries < 0:
                    raise Exception(
                        'Bug: ImportGuardHook._num_entries became negative!'
                    )
                cls._uninstall()
drop a previously created guard on ``module_name``
        if the module is not guarded, then this is a no-op.