Do not interpret -- in echo(1)

Retain -n as it is marginally useful and common.

echo.c

@@ -1,26 +1,17 @@
 /* See LICENSE file for copyright and license details. */
 #include <stdio.h>
-
+#include <string.h>
 #include "util.h"
 
-static void
-usage(void)
-{
-	eprintf("usage: %s [-n] [string ...]\n", argv0);
-}
-
 int
 main(int argc, char *argv[])
 {
 	int nflag = 0;
 
-	ARGBEGIN {
-	case 'n':
+	if (*++argv && !strcmp(*argv, "-n")) {
 		nflag = 1;
-		break;
-	default:
-		usage();
-	} ARGEND;
+		argc--, argv++;
+	}
 
 	for (; *argv; argc--, argv++)
 		putword(*argv);