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/fw/forwarder.t.cpp b/tests/daemon/fw/forwarder.t.cpp
index eef2cea..98f767f 100644
--- a/tests/daemon/fw/forwarder.t.cpp
+++ b/tests/daemon/fw/forwarder.t.cpp
@@ -34,8 +34,7 @@
 
 #include <ndn-cxx/lp/tags.hpp>
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class ForwarderFixture : public GlobalIoTimeFixture
 {
@@ -881,5 +880,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestForwarder
 BOOST_AUTO_TEST_SUITE_END() // Fw
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests