def is_model_deprecated(m):
    """
    Check if a mode is deprecated model redirection.

    A deprecated mode redirecation has only two members with a
    description starts with "Deprecated." string.
    """
    if len(m) != 2:
        return False
    if "$ref" not in m or "description" not in m:
        return False
    return m["description"].startswith("Deprecated.")