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/dummy-face.hpp b/tests/daemon/face/dummy-face.hpp
index 94b5363..8374430 100644
--- a/tests/daemon/face/dummy-face.hpp
+++ b/tests/daemon/face/dummy-face.hpp
@@ -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,
@@ -28,9 +28,7 @@
 
 #include "face/face.hpp"
 
-namespace nfd {
-namespace face {
-namespace tests {
+namespace nfd::tests {
 
 class DummyLinkService;
 
@@ -57,7 +55,7 @@
    *  \throw std::runtime_error state transition is invalid
    */
   void
-  setState(FaceState state);
+  setState(face::FaceState state);
 
   /** \brief causes the face to receive an Interest
    */
@@ -92,13 +90,6 @@
   std::vector<lp::Nack>& sentNacks;
 };
 
-} // namespace tests
-} // namespace face
-
-namespace tests {
-using nfd::face::tests::DummyFace;
-} // namespace tests
-
-} // namespace nfd
+} // namespace nfd::tests
 
 #endif // NFD_TESTS_DAEMON_FACE_DUMMY_FACE_HPP