Refactor and modernize namespace declarations

Move all unit tests to namespace nfd::tests

Delete unused header core/algorithm.hpp

Change-Id: I5591f0c5f3bb5db67f8b45fae95471f8a555ca68
diff --git a/daemon/face/lp-fragmenter.cpp b/daemon/face/lp-fragmenter.cpp
index 6b1755a..0243a48 100644
--- a/daemon/face/lp-fragmenter.cpp
+++ b/daemon/face/lp-fragmenter.cpp
@@ -28,8 +28,7 @@
 
 #include <ndn-cxx/encoding/tlv.hpp>
 
-namespace nfd {
-namespace face {
+namespace nfd::face {
 
 NFD_LOG_INIT(LpFragmenter);
 
@@ -153,5 +152,4 @@
   return os;
 }
 
-} // namespace face
-} // namespace nfd
+} // namespace nfd::face