infra-prod-setup-keys: drop inventory add

This playbook does not need to actually access the bastion host
(bridge.o.o) so does not need the inventory setup steps here.

It was pointed out in review of the prior change
(I1bbf4f1402938216401dd924da62aa869a08875b) that we could drop this
job and do this known_hosts setup in system-config for each job.
However, I think it's not a bad idea to keep a synchronization point
for the infra-prod jobs here in a trusted playbook.

Depends-On: https://review.opendev.org/c/opendev/system-config/+/807808
Change-Id: I43285bf61a2902851a15929ac3725fe131ef5b1f

playbooks/infra-prod/setup-keys.yaml

@@ -1,16 +1,5 @@
 - hosts: localhost
   tasks:
-    - name: Add bridge.o.o to inventory
-      add_host:
-        name: bridge.openstack.org
-        ansible_python_interpreter: python3
-        ansible_user: zuul
-        # Without setting ansible_host directly, mirror-workspace-git-repos
-        # gets sad because if delegate_to localhost and with add_host that
-        # ends up with ansible_host being localhost.
-        ansible_host: bridge.openstack.org
-        ansible_port: 22
-
     - name: Add bridge.o.o hostkey to known hosts
       known_hosts:
         name: bridge.openstack.org