**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
for env_var in [
            os_environment for os_environment in os.environ if os_environment.startswith('AIRFLOW__')
        ]:
            try:
                _, section, key = env_var.split('__', 2)
                opt = self._get_env_var_option(section, key)
            except ValueError:
                continue
            if not display_sensitive and env_var != 'AIRFLOW__CORE__UNIT_TEST_MODE':
                opt = '< hidden >'
            elif raw:
                opt = opt.replace('%', '%%')
            if display_source:
                opt = (opt, 'env var')
            section = section.lower()
            
            
            
            
            if section != 'kubernetes_environment_variables':
                key = key.lower()
            config_sources.setdefault(section, OrderedDict()).update({key: opt})
    @staticmethod
    def _replace_config_with_display_sources(config_sources, configs, display_source, raw):