We move the admin-revoker and expiration-mailer to using the
SA.GetRegistration RPC method instead of digging into the database
itself.
This allows the hiding of the registration model layer inside of SA, so
we can do fancy things with sha256 for the unique index inside of
it. This will happen in a later commit. See #579.
By exposing fewer details about how Registration is stored, we gain more
flexibility to fix up how its stored.
In the expiration-mailer, the performance hit for the early filtering of
mailto is likely neglibible and possibly even a benefit given the cost
of joins to the memory of MySQL.
If need be, we can built a bulk RPC layer for SA that provides the data
we need in findExpiringCertificates. It'll be easier than trying to
scale and change the storage layer underneath for each consumer.
Jeff Hodges