x/ref/runtime/internal/rpc: Don't return server errs as BadProtocol.
x/ref/runtime/internal/rpc: Don't return server errs as BadProtocol.

All database Exec errors (e.g., parser errors) where coming back
as Recv BadProtocol errors.  This change stops that behavior.
Now, Recv returns the application error (which is the same as
Finish returns).

Change-Id: Ia1372bf7cc0bfa732bf5ae69b79a579461c6126b

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref