nologin(8) does not seem to require any command line parameters,

so remove argc and argv from main() argument.

At the same time, user and tt is not likely to be changed during
execution so mark them const.

This commit should guarantee nologin to pass WARNS=6.

Tested on:	i386
MFC After:	1 month

usr.sbin/nologin/nologin.c

@@ -34,9 +34,9 @@ __FBSDID("$FreeBSD$");
 #define	MESSAGE	"This account is currently not available.\n"
 
 int
-main(int argc, char *argv[])
+main(void)
 {
-	char *user, *tt;
+	const char *user, *tt;
 
 	if ((tt = ttyname(0)) == NULL)
 		tt = "UNKNOWN";