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/mgmt/command-authenticator.t.cpp b/tests/daemon/mgmt/command-authenticator.t.cpp
index 7db02ca..051d7c9 100644
--- a/tests/daemon/mgmt/command-authenticator.t.cpp
+++ b/tests/daemon/mgmt/command-authenticator.t.cpp
@@ -29,8 +29,7 @@
 
 #include <boost/filesystem.hpp>
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class CommandAuthenticatorFixture : public CommandInterestSignerFixture
 {
@@ -468,5 +467,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestCommandAuthenticator
 BOOST_AUTO_TEST_SUITE_END() // Mgmt
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests