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/strategy-choice-entry.cpp b/daemon/table/strategy-choice-entry.cpp
index 1a1ea8e..a752e45 100644
--- a/daemon/table/strategy-choice-entry.cpp
+++ b/daemon/table/strategy-choice-entry.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  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,
@@ -26,8 +26,7 @@
 #include "strategy-choice-entry.hpp"
 #include "fw/strategy.hpp"
 
-namespace nfd {
-namespace strategy_choice {
+namespace nfd::strategy_choice {
 
 Entry::Entry(const Name& prefix)
   : m_prefix(prefix)
@@ -48,5 +47,4 @@
   m_strategy = std::move(strategy);
 }
 
-} // namespace strategy_choice
-} // namespace nfd
+} // namespace nfd::strategy_choice