Problem: deprecated poller's method in draft API

We have a deprecated method `add` in poller that contradicts purpose of a draft
API where it can change without deprecation period.

Solution: remove the method so we do not to maintain it anymore.

zmq.hpp

@@ -1050,13 +1050,6 @@ namespace zmq
 
         using handler_t = std::function<void(short)>;
 
-        ZMQ_DEPRECATED("from 4.3.0, use overload accepting handler_t instead")
-        void add (zmq::socket_t &socket, short events, std::function<void(void)> &handler)
-        {
-            add (socket, events, handler ? [&handler](short) { handler(); }
-                                         : handler_t{});
-        }
-
         void add (zmq::socket_t &socket, short events, handler_t handler)
         {
             auto it = std::end (handlers);