check_pgsql: Remove -4/-6 flags from help output

The -4/-6 options are currently not supported.

plugins/check_pgsql.c

@@ -576,7 +576,7 @@ void
 print_usage (void)
 {
 	printf ("%s\n", _("Usage:"));
-	printf ("%s [-H <host>] [-4|-6] [-P <port>] [-c <critical time>] [-w <warning time>]\n", progname);
+	printf ("%s [-H <host>] [-P <port>] [-c <critical time>] [-w <warning time>]\n", progname);
 	printf (" [-t <timeout>] [-d <database>] [-l <logname>] [-p <password>]\n"
 			"[-q <query>] [-C <critical query range>] [-W <warning query range>]\n");
 }