Revert "Fix glib-mkenum warning"

This reverts commit 247756a7d89008ee6a7d1171dc07ba22454c6034.

Was wrong.  Right fix coming.
diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index 7d60b4f..4ed458f 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -62,7 +62,9 @@
 typedef struct hb_glyph_info_t
 {
   hb_codepoint_t codepoint;
+  /*< private >*/
   hb_mask_t      mask;
+  /*< public >*/
   uint32_t       cluster;
 
   /*< private >*/