src: Remove unnecessary uses of boost::cref in make_shared and replace boost::cref/boost::ref with just cref/ref

In some cases, due to argument-dependent lookup, it is necessary to use
ndn::ref, instead of just ref.

Change-Id: I682180a007609535855f77511b49622154ad4f11
Refs: #1591
diff --git a/rib/main.cpp b/rib/main.cpp
index d74ed8d..75771b7 100644
--- a/rib/main.cpp
+++ b/rib/main.cpp
@@ -195,7 +195,7 @@
       {
         /// \todo May be try to reload config file
         signalSet.async_wait(bind(&Nrd::terminate, this, _1, _2,
-                                  boost::ref(signalSet)));
+                                  ref(signalSet)));
       }
   }
 
@@ -259,7 +259,7 @@
   signalSet.add(SIGUSR1);
   signalSet.add(SIGUSR2);
   signalSet.async_wait(bind(&Nrd::terminate, &nrdInstance, _1, _2,
-                            boost::ref(signalSet)));
+                            ndn::ref(signalSet)));
 
   try {
     nfd::getGlobalIoService().run();