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

Sorry for the noise, downstream custom builders.  Please adjust.
diff --git a/src/hb-shaper.cc b/src/hb-shaper.cc
index 660dfb2..52418c0 100644
--- a/src/hb-shaper.cc
+++ b/src/hb-shaper.cc
@@ -24,9 +24,9 @@
  * Google Author(s): Behdad Esfahbod
  */
 
-#include "hb-private.hh"
-#include "hb-shaper-private.hh"
-#include "hb-machinery-private.hh"
+#include "hb.hh"
+#include "hb-shaper.hh"
+#include "hb-machinery.hh"
 
 
 static const hb_shaper_pair_t all_shapers[] = {