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/daemon/fw/access-strategy.t.cpp b/tests/daemon/fw/access-strategy.t.cpp
index cb55cca..6664a16 100644
--- a/tests/daemon/fw/access-strategy.t.cpp
+++ b/tests/daemon/fw/access-strategy.t.cpp
@@ -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,
@@ -28,12 +28,10 @@
 #include "strategy-tester.hpp"
 #include "topology-tester.hpp"
 
-namespace nfd {
-namespace fw {
-namespace tests {
+namespace nfd::tests {
 
 // The tester is unused in this file, but it's used in various templated test suites.
-using AccessStrategyTester = StrategyTester<AccessStrategy>;
+using AccessStrategyTester = StrategyTester<fw::AccessStrategy>;
 NFD_REGISTER_STRATEGY(AccessStrategyTester);
 
 // This test suite tests AccessStrategy's behavior as a black box,
@@ -371,6 +369,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestAccessStrategy
 BOOST_AUTO_TEST_SUITE_END() // Fw
 
-} // namespace tests
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::tests