core: reimplement logging using ndn-cxx's facility

Change-Id: Ifc7c5d70a61ad405dc1f1adfa522a2c0ad1586ab
Refs: #4580
diff --git a/unit-tests.conf.sample b/unit-tests.conf.sample
index d75c19c..3ebb9f7 100644
--- a/unit-tests.conf.sample
+++ b/unit-tests.conf.sample
@@ -22,10 +22,11 @@
   ; Run:
   ;   nfd --modules
   ;
-  ; Or look for NFD_LOG_INIT(<module name>) statements in .cpp files
+  ; Or look for NFD_LOG_INIT(<module name>) statements in source files.
+  ; Note that the "nfd." prefix can be omitted.
   ;
   ; Example module-level settings:
   ;
   ; FibManager DEBUG
   ; Forwarder INFO
-}
\ No newline at end of file
+}