[CI] Drop periodics

We agreed that, due to DockerHub pull limits, it is more
appropriate to spend pull credits on real reviews than these
extra periodic runs.
This also makes us more lightweight on CI in general.

Change-Id: I5c2ee0042e9e07108a8177983fbf5fc6bb8163f0

Author: yoctozepto

zuul.d/project.yaml

@@ -60,15 +60,3 @@
         - kolla-ansible-centos8-source-upgrade
         - kolla-ansible-ubuntu-source
         - kolla-ansible-ubuntu-source-upgrade
-    periodic:
-      jobs:
-        - kolla-ansible-centos8-source-zun
-        - kolla-ansible-ubuntu-source-zun
-        - kolla-ansible-centos8-source-masakari
-        - kolla-ansible-ubuntu-source-masakari
-        - kolla-ansible-centos8-source-ironic
-        - kolla-ansible-ubuntu-source-ironic
-        - kolla-ansible-centos8-source-upgrade
-        - kolla-ansible-ubuntu-source-upgrade
-        - kolla-ansible-centos8-source-mariadb
-        - kolla-ansible-ubuntu-source-mariadb