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/tools/nfdc/strategy-choice-module.hpp b/tools/nfdc/strategy-choice-module.hpp
index 7c403a9..502d66b 100644
--- a/tools/nfdc/strategy-choice-module.hpp
+++ b/tools/nfdc/strategy-choice-module.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018,  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,
@@ -29,9 +29,7 @@
 #include "module.hpp"
 #include "command-parser.hpp"
 
-namespace nfd {
-namespace tools {
-namespace nfdc {
+namespace nfd::tools::nfdc {
 
 using ndn::nfd::StrategyChoice;
 
@@ -97,8 +95,6 @@
   std::vector<StrategyChoice> m_status;
 };
 
-} // namespace nfdc
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tools::nfdc
 
 #endif // NFD_TOOLS_NFDC_STRATEGY_CHOICE_MODULE_HPP