Clean up pub/sub test objects

--HG--
extra : amend_source : da40dbd8715b1a98b160f85ed884ff30085c9745
Replace ZMQ_Push,Pull with ZPush,Pull
Replace ZMQ_Req,Rep with ZReq,Rep
Replace ZMQ_XPub,XSub with ZXPub,XSub - however, tests for them are currently stalling - come back after C++ cleanup

--HG--
extra : amend_source : 83b8e6b72e3632845dce2325ff7b0c8bb253d7a2
Remove old socket type differentiating C++ classes
Remove obsolete zmq_subscribing_socket_thread.h
Remove old binds/connects properties from ZMQ_AbstractSocketThread