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/fib-manager.t.cpp b/tests/daemon/mgmt/fib-manager.t.cpp
index 544eda5..5ab310d 100644
--- a/tests/daemon/mgmt/fib-manager.t.cpp
+++ b/tests/daemon/mgmt/fib-manager.t.cpp
@@ -32,8 +32,7 @@
 #include <ndn-cxx/lp/tags.hpp>
 #include <ndn-cxx/mgmt/nfd/fib-entry.hpp>
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class FibManagerFixture : public ManagerFixtureWithAuthenticator
 {
@@ -446,5 +445,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestFibManager
 BOOST_AUTO_TEST_SUITE_END() // Mgmt
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests