Remove CentOS 7 based job

https://review.opendev.org/q/topic:ooo_c7_teardown is dropping
the c7 based jobs.

It also removes job definitions.

The last run https://zuul.openstack.org/builds?job_name=tripleo-ci-centos-7-undercloud-containers
was from 1 year ago.

We are removing these jobs as a part of ooo_c7_teardown[1].

[1]. https://review.opendev.org/q/topic:ooo_c7_teardown

Signed-off-by: Chandan Kumar (raukadah) <chkumar@redhat.com>
Change-Id: I94d290321213ae0e097a9ac7d472878940edbafa

zuul.d/base.yaml

@@ -1,15 +0,0 @@
-- job:
-    description: Base ansible-role-container-registry job
-    name: ansible-role-container-registry-centos-7-base
-    nodeset: centos-7
-    parent: base
-    pre-run:
-    - zuul.d/playbooks/pre.yml
-    timeout: 1800
-    voting: true
-- job:
-    description: Run molecule testing
-    name: ansible-role-container-registry-centos-7-molecule
-    parent: ansible-role-container-registry-centos-7-base
-    run:
-    - zuul.d/playbooks/run.yml

zuul.d/layout.yaml

@@ -1,14 +1,10 @@
 - project:
     check:
       jobs:
-        - ansible-role-container-registry-centos-7-molecule
         - openstack-tox-linters
-        - tripleo-ci-centos-7-undercloud-containers
     gate:
       jobs:
-        - ansible-role-container-registry-centos-7-molecule
         - openstack-tox-linters
-        - tripleo-ci-centos-7-undercloud-containers
     post:
       jobs:
         - publish-openstack-python-branch-tarball