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

Sorry for the noise, downstream custom builders.  Please adjust.
diff --git a/src/hb-ot-layout-gpos-table.hh b/src/hb-ot-layout-gpos-table.hh
index 95bc588..66767df 100644
--- a/src/hb-ot-layout-gpos-table.hh
+++ b/src/hb-ot-layout-gpos-table.hh
@@ -29,7 +29,7 @@
 #ifndef HB_OT_LAYOUT_GPOS_TABLE_HH
 #define HB_OT_LAYOUT_GPOS_TABLE_HH
 
-#include "hb-ot-layout-gsubgpos-private.hh"
+#include "hb-ot-layout-gsubgpos.hh"
 
 
 namespace OT {