Revert "fix warn unused"

- anonymous contributor

This reverts commit 7b7d404269.

src/xpub.cpp

@@ -136,7 +136,6 @@ bool zmq::xpub_t::xhas_out ()
 
 int zmq::xpub_t::xrecv (msg_t *msg_, int flags_)
 {
-    ((void)flags_);
     //  If there is at least one 
     if (pending.empty ()) {
         errno = EAGAIN;