Remove the Support of Debian 9 because Debian 9 is EOF (#10097)

* remove-debian9-support

* Add six module into openstack-cleanup/requirements.txt (#10099)

To fix tf-elastx_cleanup job which was failed with the following error:

   File "/usr/local/lib/python3.11/site-packages/keystoneauth1/identity/generic/password.py", line 16, in <module>
     from keystoneauth1.identity import v3
   File "/usr/local/lib/python3.11/site-packages/keystoneauth1/identity/v3/__init__.py", line 27, in <module>
     from keystoneauth1.identity.v3.oauth2_mtls_client_credential import *  # noqa
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   File "/usr/local/lib/python3.11/site-packages/keystoneauth1/identity/v3/oauth2_mtls_client_credential.py", line 17, in <module>
     import six
 ModuleNotFoundError: No module named 'six'

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Co-authored-by: Kenichi Omichi <ken1ohmichi@gmail.com>

roles/bootstrap-os/molecule/default/molecule.yml

@@ -29,10 +29,6 @@ platforms:
     box: almalinux/8
     cpus: 1
     memory: 512
-  - name: debian9
-    box: generic/debian9
-    cpus: 1
-    memory: 512
   - name: debian10
     box: generic/debian10
     cpus: 1