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/pit-expiry.t.cpp b/tests/daemon/fw/pit-expiry.t.cpp
index 099d031..c2b6c41 100644
--- a/tests/daemon/fw/pit-expiry.t.cpp
+++ b/tests/daemon/fw/pit-expiry.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,
@@ -31,11 +31,7 @@
 
 #include <ndn-cxx/lp/tags.hpp>
 
-namespace nfd {
-namespace fw {
-namespace tests {
-
-using namespace nfd::tests;
+namespace nfd::tests {
 
 BOOST_AUTO_TEST_SUITE(Fw)
 BOOST_FIXTURE_TEST_SUITE(TestPitExpiry, GlobalIoTimeFixture)
@@ -415,6 +411,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestPitExpiry
 BOOST_AUTO_TEST_SUITE_END() // Fw
 
-} // namespace tests
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::tests