**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 (section, key) in self.sensitive_config_values:
            opt = self._get_secret_option(section, key)
            if opt:
                if not display_sensitive:
                    opt = '< hidden >'
                if display_source:
                    opt = (opt, 'secret')
                elif raw:
                    opt = opt.replace('%', '%%')
                config_sources.setdefault(section, OrderedDict()).update({key: opt})
                del config_sources[section][key + '_secret']
    def _include_commands(self, config_sources, display_sensitive, display_source, raw):
        for (section, key) in self.sensitive_config_values:
            opt = self._get_cmd_option(section, key)
            if not opt:
                continue
            if not display_sensitive:
                opt = '< hidden >'
            if display_source:
                opt = (opt, 'cmd')
            elif raw:
                opt = opt.replace('%', '%%')
            config_sources.setdefault(section, OrderedDict()).update({key: opt})
            del config_sources[section][key + '_cmd']
    def _include_envs(self, config_sources, display_sensitive, display_source, raw):