iodine/iodined: do not print usage if no superuser

There is no value in printing the usage in this case, as the usage
doesn't give the user any hint on how to solve this issue.

Furthermore, replace the Windows implementation with an empty inline
function, which will result in no code.

Signed-off-by: Ralf Ramsauer <ralf@ramses-pyramidenbau.de>

src/common.c

@@ -101,18 +101,16 @@ int setgroups(int count, int *groups)
 }
 #endif
 
-
-void
-check_superuser(void (*usage_fn)(void))
-{
 #ifndef WINDOWS32
+void
+check_superuser(void)
+{
 	if (geteuid() != 0) {
 		warnx("Run as root and you'll be happy.\n");
-		usage_fn();
-		/* NOTREACHED */
+		exit(-1);
 	}
-#endif
 }
+#endif
 
 char *
 format_addr(struct sockaddr_storage *sockaddr, int sockaddr_len)