Remove retired training-labs repo

training-labs repo is retired now[1], this
commit removes the reference of it.

Depends-On: https://review.opendev.org/c/openstack/training-labs/+/817505

[1] http://lists.openstack.org/pipermail/openstack-discuss/2021-October/025586.html

Change-Id: I21ec3dde83a1c11b9611b3cc1df6c3f0d14d5cae

doc/upstream-training/source/slides/docs.rst

@@ -34,8 +34,7 @@ Documentation team structure
   and separate core teams for `docs-specs <https://review.opendev.org/#/admin/groups/384,members>`_
   , `contributor-guide <https://review.opendev.org/#/admin/groups/1841,members>`_
   , `security-doc <https://review.opendev.org/#/admin/groups/347,members>`_
-  , `training-guides <https://review.opendev.org/#/admin/groups/360,members>`_
-  , and `training-labs <https://review.opendev.org/#/admin/groups/1118,members>`_
+  , and `training-guides <https://review.opendev.org/#/admin/groups/360,members>`_
 
 - `Documentation cross-project liaisons <https://wiki.openstack.org/wiki/CrossProjectLiaisons#Documentation>`_
   for questions, reviews, doc bug triaging, and patching docs

labs/README.md

@@ -1,8 +0,0 @@
-Training Labs
-=============
-
-Training labs has its own repository.
-
-
-Repository: https://opendev.org/openstack/training-labs
-Wiki: https://wiki.openstack.org/wiki/Documentation/training-labs