Remove unused old job templates and experimental jobs

Ubuntu Xenial, CentOS7 and OpenSUSE 15 are all too old.

Change-Id: I0a87cc5a35e6033d670bab56d5cdc8b8312819d8
(cherry picked from commit 609ec29ac9)

.zuul.yaml

@@ -146,61 +146,6 @@
         shared:
           MULTI_KEYSTONE: True
 
-# Experimental
-- job:
-    name: keystone-dsvm-functional-federation-centos7
-    parent: keystone-dsvm-functional
-    nodeset: devstack-single-node-centos-7
-    vars:
-      devstack_localrc:
-        TEMPEST_PLUGINS: '/opt/stack/keystone-tempest-plugin'
-      devstack_services:
-        keystone-saml2-federation: true
-        tls-proxy: false
-      devstack_plugins:
-        keystone: https://opendev.org/openstack/keystone
-      zuul_copy_output:
-        /etc/shibboleth: logs
-
-# Experimental
-- job:
-    name: keystone-dsvm-functional-federation-ubuntu-xenial
-    parent: keystone-dsvm-functional
-    nodeset: openstack-single-node-xenial
-    vars:
-      devstack_localrc:
-        TEMPEST_PLUGINS: '/opt/stack/keystone-tempest-plugin'
-      devstack_services:
-        keystone-saml2-federation: true
-        tls-proxy: false
-      devstack_plugins:
-        keystone: https://opendev.org/openstack/keystone
-      zuul_copy_output:
-        /etc/shibboleth: logs
-
-# Experimental
-- job:
-    name: keystone-dsvm-py35-functional-federation-ubuntu-xenial
-    parent: keystone-dsvm-functional-federation
-    vars:
-      devstack_localrc:
-        TEMPEST_PLUGINS: '/opt/stack/keystone-tempest-plugin'
-        USE_PYTHON3: True
-      zuul_copy_output:
-        /etc/shibboleth: logs
-
-# Experimental
-# Transitional rename
-- job:
-    name: keystone-dsvm-functional-federation
-    parent: keystone-dsvm-functional-federation-ubuntu-xenial
-
-# Experimental
-# Transitional rename
-- job:
-    name: keystone-dsvm-py35-functional-federation
-    parent: keystone-dsvm-py35-functional-federation-ubuntu-xenial
-
 - project:
     templates:
       - openstack-cover-jobs
@@ -268,11 +213,3 @@
             irrelevant-files: *irrelevant-files
         - tempest-pg-full:
             irrelevant-files: *tempest-irrelevant-files
-        - tempest-full-py3-opensuse15:
-            irrelevant-files: *tempest-irrelevant-files
-        - keystone-dsvm-functional-federation-centos7:
-            irrelevant-files: *irrelevant-files
-        - keystone-dsvm-functional-federation-ubuntu-xenial:
-            irrelevant-files: *irrelevant-files
-        - keystone-dsvm-py35-functional-federation-ubuntu-xenial:
-            irrelevant-files: *irrelevant-files