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/tests/other/fw/congestion-mark-strategy.hpp b/tests/other/fw/congestion-mark-strategy.hpp
index 9b0f982..7c41f3e 100644
--- a/tests/other/fw/congestion-mark-strategy.hpp
+++ b/tests/other/fw/congestion-mark-strategy.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2021,  Regents of the University of California,
+ * Copyright (c) 2014-2022,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -28,8 +28,7 @@
 
 #include "daemon/fw/best-route-strategy.hpp"
 
-namespace nfd {
-namespace fw {
+namespace nfd::fw {
 
 /** \brief Congestion Mark integration testing strategy
  *
@@ -58,7 +57,6 @@
   bool m_shouldPreserveMark = true;
 };
 
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::fw
 
 #endif // NFD_TESTS_OTHER_FW_CONGESTION_MARK_STRATEGY_HPP