remove stale openstack/openstack-manuals/doc/training-guides

training-guides files were moved to the openstack/training-guides repo.
the original files are now stale and need to be removed.

Change-Id: Ife95a352833c822c937478b6929494868385d78d
Closes-Bug: #1329985
Merge "remove stale openstack/openstack-manuals/doc/training-guides"