patch 9.0.0328: OLD_DIGRAPHS is unused

Problem:    OLD_DIGRAPHS is unused.
Solution:   Remove OLD_DIGRAPHS.  Also drop HPUX_DIGRAPHS.
diff --git a/src/version.c b/src/version.c
index 92a9f3a..5107549 100644
--- a/src/version.c
+++ b/src/version.c
@@ -708,6 +708,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    328,
+/**/
     327,
 /**/
     326,