Remove compile time transport interface switch

- Remove the compile time check of the transport implementation.
  The transport (zeromq/nanomsg) can be chosen at run time with:
  `device.SetTransport("zeromq"); // possible values are "zeromq" and "nanomsg"`.

  For devices that use FairMQProgOptions, the transport can be configured via cmd option:
  `--transport zeromq` or `--transport nanomsg`. Default values is "zeromq".
  The device receives the configured value with:
  `device.SetTransport(config.GetValue<std::string>("transport"));`

  Old method of setting transport still works. But the NANOMSG constant is not defined.

- Remove old `fairmq/prototest` directory. It was only used as a test for protobuf.
  The protobuf part of Tutorial3 does the same (with different values).

- Fix a bug in FairMQPollerNN, where the `revents` value was not initialized.
  This caused the `poller->CheckOutput()` to trigger when it should not.

fairmq/test/req-rep/runTestRep.cxx

@@ -17,22 +17,11 @@
 #include "FairMQLogger.h"
 #include "FairMQTestRep.h"
 
-#ifdef NANOMSG
-#include "FairMQTransportFactoryNN.h"
-#else
-#include "FairMQTransportFactoryZMQ.h"
-#endif
-
 int main(int argc, char** argv)
 {
     FairMQTestRep testRep;
     testRep.CatchSignals();
-
-#ifdef NANOMSG
-    testRep.SetTransport(new FairMQTransportFactoryNN());
-#else
-    testRep.SetTransport(new FairMQTransportFactoryZMQ());
-#endif
+    testRep.SetTransport("zeromq");
 
     testRep.SetProperty(FairMQTestRep::Id, "testRep");