**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
log.info("Reading the config from %s", AIRFLOW_CONFIG)
conf = AirflowConfigParser(default_config=parameterized_config(DEFAULT_CONFIG))
conf.read(AIRFLOW_CONFIG)
if conf.has_option('core', 'AIRFLOW_HOME'):
    msg = (
        'Specifying both AIRFLOW_HOME environment variable and airflow_home '
        'in the config file is deprecated. Please use only the AIRFLOW_HOME '
        'environment variable and remove the config file entry.'
    )
    if 'AIRFLOW_HOME' in os.environ:
        warnings.warn(msg, category=DeprecationWarning)
    elif conf.get('core', 'airflow_home') == AIRFLOW_HOME:
        warnings.warn(
            'Specifying airflow_home in the config file is deprecated. As you '
            'have left it at the default value you should remove the setting '
            'from your airflow.cfg and suffer no change in behaviour.',
            category=DeprecationWarning,
        )
    else:
        AIRFLOW_HOME = conf.get('core', 'airflow_home')
        warnings.warn(msg, category=DeprecationWarning)
WEBSERVER_CONFIG = AIRFLOW_HOME + '/webserver_config.py'
if not os.path.isfile(WEBSERVER_CONFIG):
    log.info('Creating new FAB webserver config file in: %s', WEBSERVER_CONFIG)
    DEFAULT_WEBSERVER_CONFIG, _ = _read_default_config_file('default_webserver_config.py')
    with open(WEBSERVER_CONFIG, 'w') as file:
        file.write(DEFAULT_WEBSERVER_CONFIG)
if conf.getboolean('core', 'unit_test_mode'):
    conf.load_test_config()
def load_test_config():