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/table/cs-fixture.hpp b/tests/daemon/table/cs-fixture.hpp
index 82fbb7e..30273d3 100644
--- a/tests/daemon/table/cs-fixture.hpp
+++ b/tests/daemon/table/cs-fixture.hpp
@@ -33,13 +33,9 @@
 
 #include <cstring>
 
-namespace nfd {
-namespace cs {
-namespace tests {
+namespace nfd::tests {
 
-using namespace nfd::tests;
-
-#define CHECK_CS_FIND(expected) find([&] (uint32_t found) { BOOST_CHECK_EQUAL(expected, found); });
+#define CHECK_CS_FIND(expected) find([&] (uint32_t found) { BOOST_CHECK_EQUAL(expected, found); })
 
 class CsFixture : public GlobalIoTimeFixture
 {
@@ -105,8 +101,6 @@
   shared_ptr<Interest> interest;
 };
 
-} // namespace tests
-} // namespace cs
-} // namespace nfd
+} // namespace nfd::tests
 
 #endif // NFD_TESTS_DAEMON_TABLE_CS_FIXTURE_HPP