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.cpp b/daemon/table/cs-policy.cpp
index 6b24eb3..3e3fc53 100644
--- a/daemon/table/cs-policy.cpp
+++ b/daemon/table/cs-policy.cpp
@@ -32,8 +32,7 @@
 
 NFD_LOG_INIT(CsPolicy);
 
-namespace nfd {
-namespace cs {
+namespace nfd::cs {
 
 Policy::Registry&
 Policy::getRegistry()
@@ -100,5 +99,4 @@
   this->doBeforeUse(i);
 }
 
-} // namespace cs
-} // namespace nfd
+} // namespace nfd::cs