Remove centos-8/9-stream jobs on stable/yoga

The following 2 already n-v jobs have been failing:
* devstack-platform-centos-8-stream - most of 2022
* devstack-platform-centos-9-stream - last 2 months

Considering that there isn't a lot of traffic on stable/yoga
and we have a centos job in newer branches so any backport
patch gets tested there, the commit removes those 2 jobs
not to waste CI resources.

Change-Id: Id218cf2ad5fbb9cae5828972366fe85911e500b2

.zuul.yaml

@@ -635,26 +635,6 @@
 # we often have to rush things through devstack to stabilise the gate,
 # and these platforms don't have the round-the-clock support to avoid
 # becoming blockers in that situation.
-- job:
-    name: devstack-platform-centos-8-stream
-    parent: tempest-full-py3
-    description: CentOS 8 Stream platform test
-    nodeset: devstack-single-node-centos-8-stream
-    voting: false
-    timeout: 9000
-    vars:
-      configure_swap_size: 4096
-
-- job:
-    name: devstack-platform-centos-9-stream
-    parent: tempest-full-py3
-    description: CentOS 9 Stream platform test
-    nodeset: devstack-single-node-centos-9-stream
-    voting: false
-    timeout: 9000
-    vars:
-      configure_swap_size: 4096
-
 - job:
     name: devstack-platform-debian-bullseye
     parent: tempest-full-py3
@@ -780,8 +760,6 @@
         - devstack
         - devstack-ipv6
         - devstack-enforce-scope
-        - devstack-platform-centos-8-stream
-        - devstack-platform-centos-9-stream
         - devstack-platform-debian-bullseye
         - devstack-multinode
         - devstack-unit-tests