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/face-module.t.cpp b/tests/tools/nfdc/face-module.t.cpp
index d99383e..87356a1 100644
--- a/tests/tools/nfdc/face-module.t.cpp
+++ b/tests/tools/nfdc/face-module.t.cpp
@@ -28,10 +28,7 @@
 #include "execute-command-fixture.hpp"
 #include "status-fixture.hpp"
 
-namespace nfd {
-namespace tools {
-namespace nfdc {
-namespace tests {
+namespace nfd::tools::nfdc::tests {
 
 using ndn::nfd::FaceQueryFilter;
 
@@ -1162,7 +1159,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestFaceModule
 BOOST_AUTO_TEST_SUITE_END() // Nfdc
 
-} // namespace tests
-} // namespace nfdc
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tools::nfdc::tests