Remove Mitaka stable compat job, adjust filtering for Newton

We recently introduced a new Newton stable compat job [1] for projects
such as the oslo libraries.

As things are now, it is currently voting in stable/mitaka branch
reviews and it is probably not expected for Newton jobs to be passing
on Mitaka backports. Example of such failing backport here [2].

This change is analogous to the adjustments we did when Mitaka
released [3].

[1]: https://review.openstack.org/#/c/375111/
[2]: https://review.openstack.org/#/c/389190/
[3]: https://review.openstack.org/#/c/295500/

Change-Id: I04112e13ca69998c069c9e30f55e1f069f902253

jenkins/jobs/tempest-jobs.yaml

@@ -10,11 +10,6 @@
 - job-group:
     name: 'stable-compat-jobs-{name}'
     jobs:
-      - '{pipeline}-tempest-dsvm-neutron-src-{name}{job-suffix}':
-          pipeline: gate
-          node: ubuntu-trusty
-          job-suffix: '-mitaka'
-          branch-override: stable/mitaka
       - '{pipeline}-tempest-dsvm-neutron-src-{name}{job-suffix}':
           pipeline: gate
           node: ubuntu-xenial

zuul/layout.yaml

@@ -516,7 +516,6 @@ project-templates:
 
   - name: stable-compat-jobs
     check:
-      - 'gate-tempest-dsvm-neutron-src-{name}-mitaka'
       - 'gate-tempest-dsvm-neutron-src-{name}-newton'
 
   - name: lib-forward-testing-plugin
@@ -2243,8 +2242,8 @@ jobs:
     branch: ^openstack/(?!2\.4).*$
 
     # For stable compat jobs.
-  - name: ^gate-tempest-dsvm-neutron-src-.*-mitaka$
-    branch: ^(?!stable/(liberty|mitaka)).*$
+  - name: ^gate-tempest-dsvm-neutron-src-.*-newton$
+    branch: ^(?!stable/(liberty|mitaka|newton)).*$
     voting: false
 
   - name: ^gate-oslo.messaging-dsvm-functional-.*-qpid-nv$