Drop centos 8 stream jobs

CentOS 8 Stream has reached its end of life and the upstream
package repos have been removed. The CentOS nodes from Zuul and
Nodepool are being removed. See the following email announcement:

https: //lists.opendev.org/archives/list/service-announce@lists.opendev.org/thread/YHPRWKWULKJATAJZPFIZCBHS7HZJE5V2/
Change-Id: I8e1cbbb39360224f004d94abaf042b0f262c3cd4
diff --git a/.zuul.yaml b/.zuul.yaml
index e0a0b2e..2b502c7 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -307,14 +307,6 @@
         CINDER_ISCSI_HELPER: lioadm
 
 - job:
-    name: cinder-tempest-plugin-lvm-lio-barbican-centos-8-stream
-    parent: cinder-tempest-plugin-lvm-lio-barbican
-    nodeset: devstack-single-node-centos-8-stream
-    description: |
-      This jobs configures Cinder with LVM, LIO, barbican and
-      runs tempest tests and cinderlib tests on CentOS Stream 8.
-
-- job:
     name: cinder-tempest-plugin-lvm-lio-barbican-centos-9-stream
     parent: cinder-tempest-plugin-lvm-lio-barbican
     nodeset: devstack-single-node-centos-9-stream