dhcp-rogue: fix minor typo.

Change-Id: I50f58c938ec520a22859c349553452d2147039a2
diff --git a/cmds/dhcp-rogue.c b/cmds/dhcp-rogue.c
index 8d590bf..2441015 100644
--- a/cmds/dhcp-rogue.c
+++ b/cmds/dhcp-rogue.c
@@ -418,9 +418,8 @@
 
 void usage(const char *progname)
 {
-  fprintf(stderr, "usage: %s [-i br0] [-l]\n", progname);
+  fprintf(stderr, "usage: %s [-i br0]\n", progname);
   fprintf(stderr, "\t-i: name of the interface to probe for DHCP servers.\n");
-  fprintf(stderr, "\t-l: show a response from localhost\n");
   exit(1);
 }