core: drop std::function and ndn::Exclude from common.hpp, add ndn::optional

Change-Id: Ie3983d8b6f9929430efd8ada8d942e3f95755cd4
diff --git a/tests/rib/rib-manager.t.cpp b/tests/rib/rib-manager.t.cpp
index 55ae1c8..cdf1581 100644
--- a/tests/rib/rib-manager.t.cpp
+++ b/tests/rib/rib-manager.t.cpp
@@ -452,7 +452,7 @@
     Route route;
     route.faceId = ++faceId;
     route.cost = route.faceId * 10;
-    route.expires = ndn::nullopt;
+    route.expires = nullopt;
     return route;
   };