Remove container build jobs

We've kind of given up on this as an approach. Get rid of the jobs.

Depends-On: https://review.openstack.org/636018
Change-Id: I454a50349e579d0899fde1cdf7ede70ad67503e1

.zuul.yaml

@@ -1,19 +1,3 @@
-- job:
-    name: pbrx-build-container-images
-    nodeset: ubuntu-bionic
-    required-projects:
-      - openstack/pbrx
-    pre-run: playbooks/container-images/pre.yaml
-    run: playbooks/container-images/run.yaml
-
-- job:
-    name: pbrx-build-zuul-containers
-    parent: pbrx-build-container-images
-    required-projects:
-      - openstack-infra/zuul
-    vars:
-      zuul_work_dir: src/git.openstack.org/openstack-infra/zuul
-
 - project:
     templates:
       - docs-on-readthedocs
@@ -26,11 +10,9 @@
         - tox-py35
         - tox-py36:
             nodeset: ubuntu-bionic
-        - pbrx-build-zuul-containers
     gate:
       jobs:
         - tox-pep8
         - tox-py35
         - tox-py36:
             nodeset: ubuntu-bionic
-        - pbrx-build-zuul-containers