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/tools/nfdc/status-fixture.hpp b/tests/tools/nfdc/status-fixture.hpp
index f00b135..7616306 100644
--- a/tests/tools/nfdc/status-fixture.hpp
+++ b/tests/tools/nfdc/status-fixture.hpp
@@ -33,10 +33,7 @@
 
 #include <boost/test/tools/output_test_stream.hpp>
 
-namespace nfd {
-namespace tools {
-namespace nfdc {
-namespace tests {
+namespace nfd::tools::nfdc::tests {
 
 using ndn::Face;
 using ndn::KeyChain;
@@ -152,9 +149,6 @@
   return s;
 }
 
-} // namespace tests
-} // namespace nfdc
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tools::nfdc::tests
 
 #endif // NFD_TESTS_TOOLS_NFDC_STATUS_FIXTURE_HPP