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/tools/nfdc/status.cpp b/tools/nfdc/status.cpp
index a338b1d..081eea9 100644
--- a/tools/nfdc/status.cpp
+++ b/tools/nfdc/status.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,
@@ -34,9 +34,7 @@
 
 #include <ndn-cxx/security/validator-null.hpp>
 
-namespace nfd {
-namespace tools {
-namespace nfdc {
+namespace nfd::tools::nfdc {
 
 void
 reportStatus(ExecuteContext& ctx, const StatusReportOptions& options)
@@ -154,6 +152,4 @@
   parser.addAlias("cs", "info", "");
 }
 
-} // namespace nfdc
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tools::nfdc