Get rid of support of ancient signal handler return type int

Such environments are missing void type, older K&R C, and
such supports already had been removed in various places.
Furthermore, current hardcoded 'SIGNALRETURNSINT' is wrong.

cde/programs/dtlogin/dm.h

@@ -161,11 +161,7 @@
 /* Utmp rec prefix */
 #define UTMPREC_PREFIX  "dt"
 
-#ifdef SIGNALRETURNSINT
-#define SIGVAL int
-#else
 #define SIGVAL void
-#endif
 
 
 #ifndef UID_NO_CHANGE