Revert "fix warn unused"

- anonymous contributor

This reverts commit 7b7d404269.

src/sub.cpp

@@ -69,8 +69,6 @@ int zmq::sub_t::xsetsockopt (int option_, const void *optval_,
 
 int zmq::sub_t::xsend (msg_t *msg_, int flags_)
 {
-    ((void)msg_);
-    ((void)flags_);
     //  Overload the XSUB's send.
     errno = ENOTSUP;
     return -1;