rpc_util: update deprecated messages (#2545)

The status package now has `Convert()` and `Code()` utilities.

This patch updates the deprecation description for `ErrorDesc()` and
`Code()` to recommend using those functions, and forward the deprecated
functions to use the `status.Code()` and `status.Convert()` functions.

rpc_util.go

@@ -685,23 +685,17 @@ func rpcInfoFromContext(ctx context.Context) (s *rpcInfo, ok bool) {
 // Code returns the error code for err if it was produced by the rpc system.
 // Otherwise, it returns codes.Unknown.
 //
-// Deprecated: use status.FromError and Code method instead.
+// Deprecated: use status.Code instead.
 func Code(err error) codes.Code {
-	if s, ok := status.FromError(err); ok {
-		return s.Code()
-	}
-	return codes.Unknown
+	return status.Code(err)
 }
 
 // ErrorDesc returns the error description of err if it was produced by the rpc system.
 // Otherwise, it returns err.Error() or empty string when err is nil.
 //
-// Deprecated: use status.FromError and Message method instead.
+// Deprecated: use status.Convert and Message method instead.
 func ErrorDesc(err error) string {
-	if s, ok := status.FromError(err); ok {
-		return s.Message()
-	}
-	return err.Error()
+	return status.Convert(err).Message()
 }
 
 // Errorf returns an error containing an error code and a description;