**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 Config option values from Secret Backend"""
    secrets_client = get_custom_secret_backend()
    if not secrets_client:
        return None
    return secrets_client.get_config(config_key)
def _read_default_config_file(file_name: str) -> Tuple[str, str]:
    templates_dir = os.path.join(os.path.dirname(__file__), 'config_templates')
    file_path = os.path.join(templates_dir, file_name)
    with open(file_path, encoding='utf-8') as config_file:
        return config_file.read(), file_path
DEFAULT_CONFIG, DEFAULT_CONFIG_FILE_PATH = _read_default_config_file('default_airflow.cfg')
TEST_CONFIG, TEST_CONFIG_FILE_PATH = _read_default_config_file('default_test.cfg')
def default_config_yaml() -> dict:
    """
    Read Airflow configs from YAML file
    :return: Python dictionary containing configs & their info
    """
    templates_dir = os.path.join(os.path.dirname(__file__), 'config_templates')
    file_path = os.path.join(templates_dir, "config.yml")
    with open(file_path) as config_file:
        return yaml.safe_load(config_file)
class AirflowConfigParser(ConfigParser):