patch 8.1.0812: Unicode 16 feature is not useful

Problem:    Unicode 16 feature is not useful and cannot be detected.
Solution:   Remove UNICODE16.
diff --git a/src/version.c b/src/version.c
index c472ece..1114641 100644
--- a/src/version.c
+++ b/src/version.c
@@ -788,6 +788,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    812,
+/**/
     811,
 /**/
     810,