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.cpp b/daemon/fw/access-strategy.cpp
index e80c581..c2b6504 100644
--- a/daemon/fw/access-strategy.cpp
+++ b/daemon/fw/access-strategy.cpp
@@ -28,8 +28,7 @@
 #include "common/global.hpp"
 #include "common/logger.hpp"
 
-namespace nfd {
-namespace fw {
+namespace nfd::fw {
 
 NFD_LOG_INIT(AccessStrategy);
 NFD_REGISTER_STRATEGY(AccessStrategy);
@@ -278,5 +277,4 @@
   return me->insertStrategyInfo<MtInfo>(m_rttEstimatorOpts).first;
 }
 
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::fw