Raise error when unbind fails on broker

We had to stub out unbind in a few model spec files to prevent some
shared example setup from failing. Records were being created and
explicitly destroyed for the purpose of generating a set of valid
attributes. When broker api interactions are moved to background jobs,
we ought to be able to remove these stubs; the lifecycle callbacks will
merely schedule jobs for the api calls, not try to execute them.

[#56092012]