When notifying credentials of cert/grade changes using
notify_credentials, don't worry about signaling for program cert
awards. (A) We don't need that functionality right now when
backpopulating credentials records, and (B) we have other management
commands for that anyway.
notify_credentials was flattening a queryset when it shouldn't have,
which was exploding a large query all into memory. Hopefully this will
help with that.
This command will trigger old data about certificates or grades to
be sent to the Credentials service, for initial population or if
something goes wrong and we need to cover a downtime gap.
LEARNER-5378
