Remove compute node - OVN agent

Issue

• We are following this doc to remove a compute node.

• But when we try to run the step 10, the delete command returns a error message:

(overcloud) [stack@undercloud-rhel8 ~]$ openstack network agent list
+--------------------------------------+----------------------+-----------------------------+-------------------+-------+-------+-------------------------------+
| ID                                   | Agent Type           | Host                        | Availability Zone | Alive | State | Binary                        |
+--------------------------------------+----------------------+-----------------------------+-------------------+-------+-------+-------------------------------+
| 54f059bc-f3a9-44b8-ae85-7d48789dbb11 | OVN Controller agent | overcloud-compute-0.localdomain | n/a               | XXX   | UP    | ovn-controller                |
| 83ab200e-f907-401b-9e90-7bd5a09dee78 | OVN Metadata agent   | overcloud-compute-0.localdomain | n/a               | XXX   | UP    | networking-ovn-metadata-agent |

....

(overcloud) [stack@undercloud-rhel8 ~]$ openstack  network agent delete 54f059bc-f3a9-44b8-ae85-7d48789dbb11
Failed to delete network agent with ID '54f059bc-f3a9-44b8-ae85-7d48789dbb11': BadRequestException: 400: Client Error for url: http://10.10.10.10:9696/v2.0/agents/54f059bc-f3a9-44b8-ae85-7d48789dbb11, Bad agent request: OVN agents cannot be deleted.
1 of 1 network agents failed to delete.
(overcloud) [stack@undercloud-rhel8 ~]$ openstack  network agent delete 83ab200e-f907-401b-9e90-7bd5a09dee78
Failed to delete network agent with ID '83ab200e-f907-401b-9e90-7bd5a09dee78': BadRequestException: 400: Client Error for url: http://10.10.10.10:9696/v2.0/agents/83ab200e-f907-401b-9e90-7bd5a09dee78, Bad agent request: OVN agents cannot be deleted.
1 of 1 network agents failed to delete.

• We saw this message in /var/log/containers/neutron/server.log:

2020-09-11 16:59:38.128 27 INFO neutron.api.v2.resource [req-a9a852f8-0ab8-404f-b60b-0eac9e66a3a5 abfc3c368d1d4306be390a50c0980f79 66a145a66d8f4c72a84a8ee2ec13359b - default default] delete failed (client error): The server could not comply with the request since it is either malformed or otherwise incorrect.
2020-09-11 16:59:38.129 27 INFO neutron.wsgi [req-a9a852f8-0ab8-404f-b60b-0eac9e66a3a5 abfc3c368d1d4306be390a50c0980f79 66a145a66d8f4c72a84a8ee2ec13359b - default default] 172.16.2.122 "DELETE /v2.0/agents/83ab200e-f907-401b-9e90-7bd5a09dee78 HTTP/1.1" status: 400  len: 301 time: 0.3858376