patch 9.1.0600: Unused function and unused error constants

Problem:  unused function typval_compare_class() and error constants
Solution: remove function typval_compare_class() and ifdef out
          unused error constants (Dominique Pellé)

closes: #15299

Signed-off-by: Dominique Pellé <dominique.pelle@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 48c7f74..ae733c8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    600,
+/**/
     599,
 /**/
     598,