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

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

util/main-font-text.hh

diff --git a/util/main-font-text.hh b/util/main-font-text.hh
index 3390371..01bd2d4 100644
--- a/util/main-font-text.hh
+++ b/util/main-font-text.hh
@@ -27,7 +27,7 @@
 #ifndef HB_MAIN_FONT_TEXT_HH
 #define HB_MAIN_FONT_TEXT_HH
 
-#include "hb-private.hh"
+#include "hb.hh"
 #include "options.hh"
 
 /* main() body for utilities taking font and processing text.*/