While the initial version of this patch removed neutron.db.api, a
different duplicate patch [1] landed first.
This patch cleans up the remining references to neutron.db.api
including those in the docs and comments.
[1] https://review.openstack.org/#/c/635978/
Change-Id: I5f911f4c6a1fc582a9c1006ec5e2880853ff2909