Revert partial of 0ac6315212a3 ("msc: add inter-BSC and inter-MSC Handover tests")

Commit 0ac6315212a breaks all related GSUP SS tests because it require
all GSUP SS packages to have a OSMO_GSUP_MESSAGE_CLASS_USSD IE.

Change-Id: Iadbc37105fa67cf6383fb63b86ed653ccc7bddf7
diff --git a/library/GSUP_Types.ttcn b/library/GSUP_Types.ttcn
index 73f4562..7e26e19 100644
--- a/library/GSUP_Types.ttcn
+++ b/library/GSUP_Types.ttcn
@@ -1091,20 +1091,14 @@
 		tr_GSUP_IE_SessionId(sid),
 		tr_GSUP_IE_SessionState(state)
 	};
-	var integer last_idx := 3;
 
 	/* Optional SS payload */
 	if (istemplatekind(ss, "*")) {
 		ies[3] := *;
-		last_idx := last_idx + 1;
 	} else if (not istemplatekind(ss, "omit")) {
 		ies[3] := tr_GSUP_IE_SSInfo(ss);
-		last_idx := last_idx + 1;
 	}
 
-	ies[last_idx] := tr_GSUP_IE_Message_Class(OSMO_GSUP_MESSAGE_CLASS_USSD);
-	last_idx := last_idx + 1;
-
 	return ies;
 }