Remove public enum names again

As was reported to me, glib-mkenum does not understand named enums,
so remove for now.
diff --git a/src/hb-blob.h b/src/hb-blob.h
index d47cc90..360310b 100644
--- a/src/hb-blob.h
+++ b/src/hb-blob.h
@@ -36,7 +36,7 @@
 HB_BEGIN_DECLS
 
 
-typedef enum _hb_memory_mode_t {
+typedef enum {
   HB_MEMORY_MODE_DUPLICATE,
   HB_MEMORY_MODE_READONLY,
   HB_MEMORY_MODE_WRITABLE,