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/rib/readvertise/readvertise.t.cpp b/tests/daemon/rib/readvertise/readvertise.t.cpp
index ffcab71..6242dfc 100644
--- a/tests/daemon/rib/readvertise/readvertise.t.cpp
+++ b/tests/daemon/rib/readvertise/readvertise.t.cpp
@@ -34,11 +34,9 @@
 #include <boost/range/adaptor/transformed.hpp>
 #include <boost/range/algorithm/copy.hpp>
 
-namespace nfd {
-namespace rib {
-namespace tests {
+namespace nfd::tests {
 
-using namespace nfd::tests;
+using namespace nfd::rib;
 
 class DummyReadvertisePolicy : public ReadvertisePolicy
 {
@@ -300,6 +298,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestReadvertise
 BOOST_AUTO_TEST_SUITE_END() // Readvertise
 
-} // namespace tests
-} // namespace rib
-} // namespace nfd
+} // namespace nfd::tests