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/other/pit-fib-benchmark.cpp b/tests/other/pit-fib-benchmark.cpp
index c6888d1..a154297 100644
--- a/tests/other/pit-fib-benchmark.cpp
+++ b/tests/other/pit-fib-benchmark.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,
@@ -33,8 +33,7 @@
 #include <valgrind/callgrind.h>
 #endif
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class PitFibBenchmarkFixture
 {
@@ -149,5 +148,4 @@
   std::cout << time::duration_cast<time::microseconds>(t2 - t1) << std::endl;
 }
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests