**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.
tests/core/test_config_templates.py
'celery_broker_transport_options',
    'dask',
    'scheduler',
    'ldap',
    'kerberos',
    'github_enterprise',
    'admin',
    'elasticsearch',
    'elasticsearch_configs',
    'kubernetes',
    'smart_sensor',
]
DEFAULT_TEST_SECTIONS = [
    'core',
    "logging",
    'cli',
    'api',
    'operators',
    'hive',
    'webserver',
    'email',
    'smtp',
    'celery',
    'scheduler',
    'admin',
    'elasticsearch',
    'elasticsearch_configs',
    'kubernetes',
]
class TestAirflowCfg(unittest.TestCase):