Local ownCloud Group still has ldap mapping besides the LDAP server configuration was deleted

Steps to reproduce

1. Install server 9.1 and configure LDAP
2. Refresh the admin -> users page
3. Create ownCloud local group and add LDAP users:

MariaDB [oc]> select * from oc_group_user;
+----------+--------------------+
| gid      | uid                |
+----------+--------------------+
| Carloses | Athanasios_Janik   |
| Carloses | Benjamin_Holzer    |
| Carloses | Bertha_Gruner      |
| Carloses | Brandi_Dengler     |
| Carloses | Carola_Klages      |
| Carloses | Caterina_Thielen   |
| Carloses | Charles_Reinhard   |
| Carloses | Cindy_Diefenbach   |
| Carloses | Dirk_Mewes         |
| Carloses | Ellen_Arnold       |
| Carloses | Ellinor_Koppe      |
| Carloses | Ercan_Gerhards     |
| Carloses | Ernst-August_Flach |
| admin    | admin              |
+----------+--------------------+

1. Delete LDAP configuration
2. Run cron.php
3. Users are still in the database table.

Expected behaviour

Users are deleted from the group after deleting

Actual behaviour

Users are still in the database table oc_group_user and displayed in the user interface:

MariaDB [oc]> select * from oc_group_user;
+----------+--------------------+
| gid      | uid                |
+----------+--------------------+
| Carloses | Athanasios_Janik   |
| Carloses | Benjamin_Holzer    |
| Carloses | Bertha_Gruner      |
| Carloses | Brandi_Dengler     |
| Carloses | Carola_Klages      |
| Carloses | Caterina_Thielen   |
| Carloses | Charles_Reinhard   |
| Carloses | Cindy_Diefenbach   |
| Carloses | Dirk_Mewes         |
| Carloses | Ellen_Arnold       |
| Carloses | Ellinor_Koppe      |
| Carloses | Ercan_Gerhards     |
| Carloses | Ernst-August_Flach |
| admin    | admin              |
+----------+--------------------+

Server configuration

ownCloud version: (see ownCloud admin page)
9.1.