db: Remove legacy placement models
db: Remove legacy placement models

These are now managed separately via the extracted placement project. We
no longer need to include them in the API database.

Change-Id: If18344034b31d9f6168e7a1c7d49bdcb3d53113e
Signed-off-by: Stephen Finucane <4725dc7f3632bf126d9fbdc30c347e91e8d2fe16@redhat.com>

mahak/nova,openstack/nova,mahak/nova,mahak/nova,openstack/nova,openstack/nova