**Apache Airflow version**: 2.0.0b* / master


**What happened**:

`[ldap]` section in `airflow.cfg` is not applicable anymore in 2.0 and `master`, because the LDAP authentication (for webserver and API) is handled by FAB, and the configuration for this is handled by `webserver_config.py` file.

![airflow_–_default_airflow_cfg](https://user-images.githubusercontent.com/11539188/99289209-ef210700-283c-11eb-948e-16811ba09293.png)


**What you expected to happen**:

The `[ldap]` section should be removed from `airflow/config_templates/default_airflow.cfg` and `airflow/config_templates/config.yml` (and some other applicable files).

Otherwise leaving this section there will be a big confusion for users.
airflow/configuration.py
"""Get Secret Backend if defined in airflow.cfg"""
    secrets_backend_cls = conf.getimport(section='secrets', key='backend')
    if secrets_backend_cls:
        try:
            alternative_secrets_config_dict = json.loads(
                conf.get(section='secrets', key='backend_kwargs', fallback='{}')
            )
        except JSONDecodeError:
            alternative_secrets_config_dict = {}
        return secrets_backend_cls(**alternative_secrets_config_dict)
    return None
def initialize_secrets_backends() -> List[BaseSecretsBackend]:
    """
    * import secrets backend classes
    * instantiate them and return them in a list
    """
    backend_list = []
    custom_secret_backend = get_custom_secret_backend()
    if custom_secret_backend is not None:
        backend_list.append(custom_secret_backend)
    for class_name in DEFAULT_SECRETS_SEARCH_PATH:
        secrets_backend_cls = import_string(class_name)
        backend_list.append(secrets_backend_cls())
    return backend_list
secrets_backend_list = initialize_secrets_backends()