RA: Simplify sending validation records to the SA

[aarongable]

Remove unnecessary abstraction from the RA as it receives validation records and problems from the VA, and forwards them to the SA for storage. Instead of converting everything from protobufs to core objects, then modifying other core objects in place, then extracting fields from those core objects to convert back to protobufs... simply pass through the existing protobufs unchanged. This removes about 40 lines from the RA, including a whole helper function, greatly simplifying its asynchronous background validation goroutine.

As a result of deleting the helper function, we lose some test coverage of a particular double-validation race case. But that test never should have been in the RA in the first place (it's asserting that the RA gets the right error code back from the SA), so replace it with an equivalent test in the SA.

[jsha]

Generally looks good; one question / request about retaining a certain log line.