Switch to a single upb_Decode.

upb/json_encode.c

diff --git a/upb/json_encode.c b/upb/json_encode.c
index 048b855..a63b3c6 100644
--- a/upb/json_encode.c
+++ b/upb/json_encode.c
@@ -383,7 +383,7 @@
   upb_Arena* arena = jsonenc_arena(e);
   upb_Message* any = upb_Message_New(any_m, arena);
 
-  if (upb_decode(value.data, value.size, any, any_layout, arena) !=
+  if (upb_Decode(value.data, value.size, any, any_layout, NULL, 0, arena) !=
       kUpb_DecodeStatus_Ok) {
     jsonenc_err(e, "Error decoding message in Any");
   }