Problem: stream_engine_t::_as_server is not used

Solution: remove it

src/stream_engine.cpp

@@ -67,7 +67,6 @@ zmq::stream_engine_t::stream_engine_t (fd_t fd_,
                                        const options_t &options_,
                                        const std::string &endpoint_) :
     _s (fd_),
-    _as_server (false),
     _handle (static_cast<handle_t> (NULL)),
     _inpos (NULL),
     _insize (0),

src/stream_engine.hpp

@@ -145,9 +145,6 @@ class stream_engine_t : public io_object_t, public i_engine
     //  Underlying socket.
     fd_t _s;
 
-    //  True iff this is server's engine.
-    bool _as_server;
-
     msg_t _tx_msg;
     //  Need to store PING payload for PONG
     msg_t _pong_msg;