Rename hb-*private.hh to hb-*.hh

Sorry for the noise, downstream custom builders.  Please adjust.
diff --git a/src/hb-buffer-deserialize-json.hh b/src/hb-buffer-deserialize-json.hh
index 380f3c5..1f9e2e9 100644
--- a/src/hb-buffer-deserialize-json.hh
+++ b/src/hb-buffer-deserialize-json.hh
@@ -29,7 +29,7 @@
 #ifndef HB_BUFFER_DESERIALIZE_JSON_HH
 #define HB_BUFFER_DESERIALIZE_JSON_HH
 
-#include "hb-private.hh"
+#include "hb.hh"
 
 
 #line 36 "hb-buffer-deserialize-json.hh"