[stable-only][CI] Drop periodic jobs

We want to run these only on the master branch, need to clean up after
branching.

Change-Id: I42a651e9d07485c7a3e61fcc2380e33fb4ee6b0b

.zuul.yaml

@@ -960,16 +960,3 @@
               - ^.*\.rst$
               - ^doc/.*$
         - devstack-no-tls-proxy
-    periodic:
-      jobs:
-        - devstack-no-tls-proxy
-    periodic-weekly:
-      jobs:
-        - devstack-platform-centos-9-stream
-        - devstack-platform-debian-bookworm
-        - devstack-platform-debian-bullseye
-        - devstack-platform-rocky-blue-onyx
-        - devstack-platform-ubuntu-jammy-ovn-source
-        - devstack-platform-ubuntu-jammy-ovs
-        - devstack-platform-openEuler-22.03-ovn-source
-        - devstack-platform-openEuler-22.03-ovs