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/strategy-instantiation.t.cpp b/tests/daemon/fw/strategy-instantiation.t.cpp
index 3ce458a..12c13a1 100644
--- a/tests/daemon/fw/strategy-instantiation.t.cpp
+++ b/tests/daemon/fw/strategy-instantiation.t.cpp
@@ -39,9 +39,9 @@
 
 #include <boost/mpl/vector.hpp>
 
-namespace nfd {
-namespace fw {
-namespace tests {
+namespace nfd::tests {
+
+using namespace nfd::fw;
 
 BOOST_AUTO_TEST_SUITE(Fw)
 BOOST_AUTO_TEST_SUITE(TestStrategyInstantiation)
@@ -202,6 +202,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestStrategyInstantiation
 BOOST_AUTO_TEST_SUITE_END() // Fw
 
-} // namespace tests
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::tests