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

Sorry for the noise, downstream custom builders.  Please adjust.
diff --git a/src/hb-ot-os2-table.hh b/src/hb-ot-os2-table.hh
index 56bbab7..c5ad803 100644
--- a/src/hb-ot-os2-table.hh
+++ b/src/hb-ot-os2-table.hh
@@ -27,7 +27,7 @@
 #ifndef HB_OT_OS2_TABLE_HH
 #define HB_OT_OS2_TABLE_HH
 
-#include "hb-open-type-private.hh"
+#include "hb-open-type.hh"
 #include "hb-ot-os2-unicode-ranges.hh"
 #include "hb-subset-plan.hh"