**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
if section == deprecated_section:
            warnings.warn(
                'The {old} option in [{section}] has been renamed to {new} - the old '
                'setting has been used, but please update your config.'.format(
                    old=deprecated_name,
                    new=key,
                    section=section,
                ),
                DeprecationWarning,
                stacklevel=3,
            )
        else:
            warnings.warn(
                'The {old_key} option in [{old_section}] has been moved to the {new_key} option in '
                '[{new_section}] - the old setting has been used, but please update your config.'.format(
                    old_section=deprecated_section,
                    old_key=deprecated_name,
                    new_key=key,
                    new_section=section,
                ),
                DeprecationWarning,
                stacklevel=3,
            )
def get_airflow_home():