Retire mitaka translation sync

openstack-manuals is the only repo that has mitaka translations set up
but the project is since some time read-only in zanata. Thus, remove the
now unneeded job and remove all unused templates.

Change-Id: I513ce52fa3bd31e4a7cf53fc412cc5addcf98a65

jenkins/jobs/projects.yaml

@@ -9328,7 +9328,6 @@
       - openstack-doc-jobs
       - openstack-releasenotes-jobs
       - manual-translation-jobs
-      - translation-jobs-mitaka
       - translation-jobs-newton
       - translation-jobs-ocata
       - gate-{name}-tox-{envlist}-{node}:

jenkins/jobs/translation-jobs.yaml

@@ -65,13 +65,6 @@
       - '{name}-upstream-translation-update'
       - '{name}-propose-translation-update{suffix}'
 
-- job-group:
-    name: translation-jobs-mitaka
-    suffix: '-mitaka'
-    branch: stable/mitaka
-    jobs:
-      - '{name}-propose-translation-update{suffix}'
-
 - job-group:
     name: translation-jobs-newton
     suffix: '-newton'

zuul/layout.yaml

@@ -662,10 +662,6 @@ project-templates:
     periodic:
       - '{name}-propose-translation-update'
 
-  - name: translation-jobs-mitaka
-    periodic:
-      - '{name}-propose-translation-update-mitaka'
-
   - name: translation-jobs-newton
     periodic:
       - '{name}-propose-translation-update-newton'
@@ -14357,7 +14353,6 @@ projects:
       - name: merge-check
       - name: openstack-doc-rst-gate
       - name: openstack-doc-translation
-      - name: translation-jobs-mitaka
       - name: translation-jobs-newton
       - name: translation-jobs-ocata
       - name: release-notes-jobs