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-scope-control.t.cpp b/tests/daemon/fw/strategy-scope-control.t.cpp
index 86e9540..d44460f 100644
--- a/tests/daemon/fw/strategy-scope-control.t.cpp
+++ b/tests/daemon/fw/strategy-scope-control.t.cpp
@@ -41,9 +41,9 @@
 
 #include <boost/mpl/vector.hpp>
 
-namespace nfd {
-namespace fw {
-namespace tests {
+namespace nfd::tests {
+
+using namespace nfd::fw;
 
 template<typename S>
 class StrategyScopeControlFixture : public GlobalIoTimeFixture
@@ -275,6 +275,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestStrategyScopeControl
 BOOST_AUTO_TEST_SUITE_END() // Fw
 
-} // namespace tests
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::tests