**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
"""
    Generates a configuration from the provided template + variables defined in
    current scope
    :param template: a config content templated with {{variables}}
    """
    all_vars = {k: v for d in [globals(), locals()] for k, v in d.items()}
    return template.format(**all_vars)  
def get_airflow_test_config(airflow_home):
    """Get path to unittests.cfg"""
    if 'AIRFLOW_TEST_CONFIG' not in os.environ:
        return os.path.join(airflow_home, 'unittests.cfg')
    return expand_env_var(os.environ['AIRFLOW_TEST_CONFIG'])
TEST_CONFIG_FILE = get_airflow_test_config(AIRFLOW_HOME)
if not os.path.isfile(TEST_CONFIG_FILE) or not os.path.isfile(AIRFLOW_CONFIG):
    FERNET_KEY = Fernet.generate_key().decode()
else:
    FERNET_KEY = ''
SECRET_KEY = b64encode(os.urandom(16)).decode('utf-8')
TEMPLATE_START = '# ----------------------- TEMPLATE BEGINS HERE -----------------------'
if not os.path.isfile(TEST_CONFIG_FILE):
    log.info('Creating new Airflow config file for unit tests in: %s', TEST_CONFIG_FILE)
    with open(TEST_CONFIG_FILE, 'w') as file:
        cfg = parameterized_config(TEST_CONFIG)
        file.write(cfg.split(TEMPLATE_START)[-1].strip())
if not os.path.isfile(AIRFLOW_CONFIG):
    log.info('Creating new Airflow config file in: %s', AIRFLOW_CONFIG)
    with open(AIRFLOW_CONFIG, 'w') as file:
        cfg = parameterized_config(DEFAULT_CONFIG)
        cfg = cfg.split(TEMPLATE_START)[-1].strip()
        file.write(cfg)