Drop CentOS 7 wheel builds and bindep fallback check job

We're working through the removal of CentOS 7. Enough time has passed
since we announced the removal that we can go ahead and start removing
some of the less important supporting infrastructure like fallback
bindep testing checks and wheel building and caching/mirroring. Go ahead
and do this cleanup.

Change-Id: I07be885c5a5641a345d052e2157a19299cfbbbcf

zuul.d/jobs.yaml

@@ -852,27 +852,6 @@
       - name: afs
         secret: afsadmin_keytab
 
-- job:
-    name: publish-wheel-cache-centos-7
-    description: |
-      Publish CentOS 7 wheels for OpenStack CI mirrors.
-    parent: build-wheel-cache-centos-7
-    pre-run: playbooks/openafs-client/setup.yaml
-    post-run: playbooks/publish/wheel-mirror.yaml
-    allowed-projects:
-      - openstack/requirements
-    final: true
-    secrets:
-      - name: afs
-        secret: wheel_keytab
-
-- job:
-    name: release-wheel-cache-centos-7
-    parent: release-wheel-cache
-    final: true
-    vars:
-      wheel_volume: 'mirror.wheel.cent7x64'
-
 - job:
     name: publish-wheel-cache-centos-8-stream
     description: |
@@ -1286,16 +1265,6 @@
       - nodepool/elements/bindep-fallback.txt
       - playbooks/bindep-fallback/run.yaml
 
-- job:
-    name: project-config-bindep-fallback-centos-7
-    parent: project-config-bindep-fallback
-    description: |
-      Check installation of binary packages for file
-      nodepool/elements/bindep-fallback.txt.
-
-      The testing is done for CentOS 7.
-    nodeset: centos-7
-
 - job:
     name: project-config-bindep-fallback-ubuntu-xenial
     parent: project-config-bindep-fallback

zuul.d/projects.yaml

@@ -3631,7 +3631,6 @@
               - tox.ini
         - project-config-irc-access
         - project-config-nodepool
-        - project-config-bindep-fallback-centos-7
         - project-config-bindep-fallback-ubuntu-xenial
     gate:
       jobs:
@@ -3651,7 +3650,6 @@
             files: *infra-docs-index
         - project-config-irc-access
         - project-config-nodepool
-        - project-config-bindep-fallback-centos-7
         - project-config-bindep-fallback-ubuntu-xenial
     deploy:
       jobs:
@@ -4294,10 +4292,6 @@
             branches: master
     periodic:
       jobs:
-        - publish-wheel-cache-centos-7
-        - release-wheel-cache-centos-7:
-            dependencies:
-              - name: publish-wheel-cache-centos-7
         - publish-wheel-cache-centos-8-stream
         - release-wheel-cache-centos-8-stream:
             dependencies: