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

Sorry for the noise, downstream custom builders.  Please adjust.

src/hb-graphite2.cc

diff --git a/src/hb-graphite2.cc b/src/hb-graphite2.cc
index 1f42a36..817278f 100644
--- a/src/hb-graphite2.cc
+++ b/src/hb-graphite2.cc
@@ -27,7 +27,7 @@
  */
 
 #define HB_SHAPER graphite2
-#include "hb-shaper-impl-private.hh"
+#include "hb-shaper-impl.hh"
 
 #include "hb-graphite2.h"