**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
#
#
import configparser
import os
import unittest
from parameterized import parameterized
from tests.test_utils import AIRFLOW_MAIN_FOLDER
CONFIG_TEMPLATES_FOLDER = os.path.join(AIRFLOW_MAIN_FOLDER, "airflow", "config_templates")
DEFAULT_AIRFLOW_SECTIONS = [
    'core',
    "logging",
    "metrics",
    'secrets',
    'cli',
    'debug',
    'api',
    'lineage',
    'atlas',
    'operators',
    'hive',
    'webserver',
    'email',
    'smtp',
    'sentry',
    'celery_kubernetes_executor',
    'celery',