veyron/tools/identity: Fix flag documentation.

Change-Id: I96be73fa66a612e70dd4ba6dc4a146beb901e096
diff --git a/tools/identity/main.go b/tools/identity/main.go
index ca26c74..9ddc3f6 100644
--- a/tools/identity/main.go
+++ b/tools/identity/main.go
@@ -122,7 +122,7 @@
 The identity of the tool can be specified with the --with flag:
 bless --with /tmp/id /tmp/blessee batman
 `,
-		ArgsName: "<file> <name> [--with=<file>]",
+		ArgsName: "<file> <name>",
 		ArgsLong: `
 <file> is the name of the file containing a base64-vom encoded security.PublicID
 or security.PrivateID