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/face/udp-factory.t.cpp b/tests/daemon/face/udp-factory.t.cpp
index e2788f5..c243ddc 100644
--- a/tests/daemon/face/udp-factory.t.cpp
+++ b/tests/daemon/face/udp-factory.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,
@@ -30,9 +30,10 @@
 
 #include <boost/algorithm/string/replace.hpp>
 
-namespace nfd {
-namespace face {
-namespace tests {
+namespace nfd::tests {
+
+using face::UdpChannel;
+using face::UdpFactory;
 
 class UdpFactoryFixture : public FaceSystemFactoryFixture<UdpFactory>
 {
@@ -1114,6 +1115,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestUdpFactory
 BOOST_AUTO_TEST_SUITE_END() // Face
 
-} // namespace tests
-} // namespace face
-} // namespace nfd
+} // namespace nfd::tests