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/unsolicited-data-policy.t.cpp b/tests/daemon/fw/unsolicited-data-policy.t.cpp
index 77722c7..ee5ae77 100644
--- a/tests/daemon/fw/unsolicited-data-policy.t.cpp
+++ b/tests/daemon/fw/unsolicited-data-policy.t.cpp
@@ -33,11 +33,9 @@
 #include <boost/logic/tribool.hpp>
 #include <boost/mpl/vector.hpp>
 
-namespace nfd {
-namespace fw {
-namespace tests {
+namespace nfd::tests {
 
-using namespace nfd::tests;
+using namespace nfd::fw;
 
 class UnsolicitedDataPolicyFixture : public GlobalIoTimeFixture
 {
@@ -131,6 +129,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestUnsolicitedDataPolicy
 BOOST_AUTO_TEST_SUITE_END() // Fw
 
-} // namespace tests
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::tests