Fix Zun Docker runtime selection

Per [1] Docker uses API version 1.26 since daemon version 1.13.1.
Kolla Ansible forced a limit on the Docker API version reported
to Zun of 1.24 which was surprising users and preventing
usage of Docker runtime selection via Zun.
The default of Zun is 1.26 [2] which enables runtime selection.
Zun does not use this parameter for anything else atm.

[1] https://docs.docker.com/engine/api/v1.26/#section/Versioning
[2] https://review.opendev.org/490794

Change-Id: Ide6eb4c2b079cf35e633ad6a04db1587e40e7633
Closes-bug: #1859176

ansible/roles/zun/templates/zun.conf.j2

@@ -111,7 +111,6 @@ wsproxy_port = {{ zun_wsproxy_port }}
 base_url = ws://{{ kolla_external_fqdn | put_address_in_context('url') }}:{{ zun_wsproxy_port }}
 
 [docker]
-docker_remote_api_version = 1.24
 api_url = tcp://{{ api_interface_address | put_address_in_context('url') }}:2375
 docker_remote_api_host = {{ api_interface_address }}
 docker_remote_api_port = 2375