Remove centos-8 role integration testing

This testing is primarily for the openafs role. We may need
https://review.opendev.org/c/openstack/openstack-zuul-jobs/+/824236 to
land first and update packages specifically for centos-8-stream before
this is mergeable. But CentOS 8 is EOL so we don't have much choice.

Change-Id: Idbd85c8f49cd169ee17f1b09db2de8bd36a52950

zuul.d/system-config-roles.yaml

@@ -136,30 +136,6 @@
           nodes:
             - base
 
-- job:
-    name: system-config-zuul-role-integration-centos-8
-    parent: system-config-zuul-role-integration
-    nodeset:
-      nodes:
-        - name: base
-          label: centos-8
-      groups:
-        - name: openafs
-          nodes:
-            - base
-
-- job:
-    name: system-config-zuul-role-integration-centos-8-arm64
-    parent: system-config-zuul-role-integration
-    nodeset:
-      nodes:
-        - name: base
-          label: centos-8-arm64
-      groups:
-        - name: openafs
-          nodes:
-            - base
-
 - job:
     name: system-config-zuul-role-integration-centos-8-stream
     parent: system-config-zuul-role-integration
@@ -197,8 +173,6 @@
         - system-config-zuul-role-integration-debian-buster-arm64
         - system-config-zuul-role-integration-debian-bullseye
         - system-config-zuul-role-integration-debian-bullseye-arm64
-        - system-config-zuul-role-integration-centos-8
-        - system-config-zuul-role-integration-centos-8-arm64
         - system-config-zuul-role-integration-centos-8-stream
         - system-config-zuul-role-integration-centos-8-stream-arm64
     gate:
@@ -212,7 +186,5 @@
         - system-config-zuul-role-integration-debian-buster-arm64
         - system-config-zuul-role-integration-debian-bullseye
         - system-config-zuul-role-integration-debian-bullseye-arm64
-        - system-config-zuul-role-integration-centos-8
-        - system-config-zuul-role-integration-centos-8-arm64
         - system-config-zuul-role-integration-centos-8-stream
         - system-config-zuul-role-integration-centos-8-stream-arm64