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-common-fixture.cpp b/tests/daemon/mgmt/manager-common-fixture.cpp
index 3188ee4..8be600c 100644
--- a/tests/daemon/mgmt/manager-common-fixture.cpp
+++ b/tests/daemon/mgmt/manager-common-fixture.cpp
@@ -25,8 +25,7 @@
 
 #include "manager-common-fixture.hpp"
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 CommandInterestSignerFixture::CommandInterestSignerFixture()
   : m_signer(m_keyChain)
@@ -212,5 +211,4 @@
   cf.parse(config, false, "ManagerCommonFixture.authenticator.conf");
 }
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests