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/table/cs-policy.hpp b/daemon/table/cs-policy.hpp
index 9a4c6ed..de4c89c 100644
--- a/daemon/table/cs-policy.hpp
+++ b/daemon/table/cs-policy.hpp
@@ -28,8 +28,7 @@
 
 #include "cs-entry.hpp"
 
-namespace nfd {
-namespace cs {
+namespace nfd::cs {
 
 class Cs;
 
@@ -206,8 +205,7 @@
   Cs* m_cs;
 };
 
-} // namespace cs
-} // namespace nfd
+} // namespace nfd::cs
 
 /** \brief registers a CS policy
  *  \param P a subclass of nfd::cs::Policy