Move serdes deserialization out of DagsterGrpcClient

Summary: Doing this in the callsite instead gives us more flexibility with back-compat, since we might just want to pass through the results of a gRPC client in some contexts without deserializing it.

Test Plan: BK

Reviewers: alangenfeld, max, johann

Reviewed By: max

Differential Revision: https://dagster.phacility.com/D8940