Update stable branches jobs on master gate

we have stable/xena and stable/yoga also present
and supported so we should add their job on master
gate to keep branchless tempest plugins compatible
to stable branch.

This also removes the old EM stable branches which are
train, ussuri, and victoria jobs.

Ref: Tempest plugins guide for stable branch testing:
- https://docs.openstack.org/tempest/latest/stable_branch_testing_policy.html

Change-Id: I56aaabe6d4a228dfc9434e9d0c163251ff64c279

.zuul.yaml

@@ -1,47 +1,12 @@
 - job:
-    name: heat-functional-convg-stein
-    parent: heat-functional-convg-mysql-lbaasv2-py3
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/stein
-    vars:
-      branch_override: stable/stein
-
-- job:
-    name: heat-functional-orig-stein
-    parent: heat-functional-orig-mysql-lbaasv2
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/stein
-    vars:
-      branch_override: stable/stein
-      use_python3: 1
-
-- job:
-    name: heat-functional-convg-train
-    parent: heat-functional-convg-mysql-lbaasv2-py3
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/train
-    vars:
-      branch_override: stable/train
-
-- job:
-    name: heat-functional-orig-train
-    parent: heat-functional-orig-mysql-lbaasv2
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/train
-    vars:
-      branch_override: stable/train
-      use_python3: 1
-
-- job:
-    name: heat-functional-ussuri
+    name: heat-functional-yoga
     parent: heat-functional
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/ussuri
+    override-checkout: stable/yoga
 
 - job:
-    name: heat-functional-victoria
+    name: heat-functional-xena
     parent: heat-functional
-    override-checkout: stable/victoria
+    override-checkout: stable/xena
 
 - job:
     name: heat-functional-wallaby
@@ -56,10 +21,8 @@
       jobs:
         - heat-functional
         - heat-functional-legacy
-        - heat-functional-convg-train
-        - heat-functional-orig-train
-        - heat-functional-ussuri
-        - heat-functional-victoria
+        - heat-functional-yoga
+        - heat-functional-xena
         - heat-functional-wallaby
     gate:
       queue: heat