[ORC] Rename blobSerializationRoundTrip, drop explicit arg types on calls.

Renames the blobSerializationRoundTrip test helper function to
spsSerializationRoundTrip ('blob' was the placeholder name for the serialization
scheme during prototyping, this function was missed when renaming everything
for the mainline). Also drops explicit template arguments at call sites where
they can be inferred (and are obvious) from the call argument type.