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/fw/access-strategy.hpp b/daemon/fw/access-strategy.hpp
index 1aaa5ed..c33ad5c 100644
--- a/daemon/fw/access-strategy.hpp
+++ b/daemon/fw/access-strategy.hpp
@@ -33,8 +33,7 @@
 
 #include <unordered_map>
 
-namespace nfd {
-namespace fw {
+namespace nfd::fw {
 
 /** \brief Access Router strategy
  *
@@ -173,7 +172,6 @@
   signal::ScopedConnection m_removeFaceConn;
 };
 
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::fw
 
 #endif // NFD_DAEMON_FW_ACCESS_STRATEGY_HPP