Use upb_sink_putunknown for reserve unknown

upb/pb/decoder.c

@@ -599,14 +599,7 @@ have_tag:
     }
 
     if (d->top->groupnum >= 0) {
-      addunknown = (upb_unknown_handlerfunc *)upb_handlers_gethandler(
+      upb_sink_putunknown(&d->top->sink, d->checkpoint, d->ptr - d->checkpoint);
-          (d->top->sink).handlers, UPB_UNKNOWN_SELECTOR);
-      if (addunknown != NULL) {
-        hd = upb_handlers_gethandlerdata((d->top->sink).handlers,
-                                         UPB_UNKNOWN_SELECTOR);
-        addunknown((d->top->sink).closure, hd, d->checkpoint,
-                   d->ptr - d->checkpoint);
-      }
       return DECODE_OK;
     }