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/mgmt/manager-base.t.cpp b/tests/daemon/mgmt/manager-base.t.cpp
index a70784c..dba2dd8 100644
--- a/tests/daemon/mgmt/manager-base.t.cpp
+++ b/tests/daemon/mgmt/manager-base.t.cpp
@@ -32,8 +32,7 @@
 #include <ndn-cxx/security/pib/key.hpp>
 #include <ndn-cxx/security/pib/pib.hpp>
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class TestCommandVoidParameters : public ControlCommand
 {
@@ -168,5 +167,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestManagerBase
 BOOST_AUTO_TEST_SUITE_END() // Mgmt
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests