Fix generate fencing command

On master this command is currently broken:
(undercloud) [stack@undercloud ~]$ openstack overcloud generate fencing instackenv.json --output fencing.yaml
Invalid input [name=generate_fencing_parameters, class=DirectWorkflowSpec, missing=['os_auth', 'fence_action']]

The reason for this is that via (A)
I63f3a579af5aa70080f8c9cdd5eb0e8f5b3d17da (Add workflow to generate
fencing parameters) we moved to use a workflow in order to generate
fencing parameters. This workflow took a bunch of inputs which we then
deprecated via two different ways:

(B) os_auth
https://review.openstack.org/#/c/570349/ and
https://review.openstack.org/#/c/567896/ we removed some for pxe_ssh but
we did not do it fully in the workbooks

(C) fence_action
Same goes for https://review.openstack.org/#/c/550028/ and
https://review.openstack.org/#/c/556211/ we removed fence_action but
since the workflow still used it as a parameter we broke things

Problem is that the review at (A) got proposed before(B) and (C), but
was merged after them. So it was never amended to account for the
changes introduced in (B) and (C). This change amends things so that
the command works correctly again:
(undercloud) [stack@undercloud ~]$ openstack overcloud generate fencing instackenv.json --output fencing.yaml
(undercloud) [stack@undercloud ~]$ ls -l fencing.yaml
-rw-rw-r--. 1 stack stack 513 Jun 28 15:46 fencing.yaml

Change-Id: I0262c493c217b64891e7da1bb3853b0d1366faef
Closes-Bug: #1779168

workbooks/parameters.yaml

@@ -10,9 +10,6 @@ workflows:
       a deployment.
     input:
       - nodes_json
-      # TODO(dtantsur): remove in Stein (after it is no longer used)
-      - os_auth
-      - fence_action
       - delay
       - ipmi_level
       - ipmi_cipher
@@ -30,7 +27,6 @@ workflows:
         action: tripleo.parameters.generate_fencing
         input:
           nodes_json: <% $.nodes_json %>
-          fence_action: <% $.fence_action %>
           delay: <% $.delay %>
           ipmi_level: <% $.ipmi_level %>
           ipmi_cipher: <% $.ipmi_cipher %>