Neutron-LBaaS has now been retired and there will be no Train
release[1]. This patch removes the neutron-lbaas API reference and
various other references to Neutron-LBaaS from neutron-lib.
[1] https://review.opendev.org/658494
Depends-On: https://review.opendev.org/665838
Related-Bug: #1833125
Change-Id: I0200abba2bca07a610839ba4fa8e2d9f2fa82218