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/tools/mock-nfd-mgmt-fixture.hpp b/tests/tools/mock-nfd-mgmt-fixture.hpp
index ec98657..3aa106b 100644
--- a/tests/tools/mock-nfd-mgmt-fixture.hpp
+++ b/tests/tools/mock-nfd-mgmt-fixture.hpp
@@ -36,14 +36,12 @@
 
 #include <boost/concept/assert.hpp>
 
-namespace nfd {
-namespace tools {
-namespace tests {
+namespace nfd::tests {
 
-using namespace nfd::tests;
 using ndn::nfd::ControlParameters;
 
-/** \brief Fixture to emulate NFD management.
+/**
+ * \brief Fixture to emulate NFD management.
  */
 class MockNfdMgmtFixture : public IoFixture, public KeyChainFixture
 {
@@ -210,9 +208,7 @@
   std::function<void(const Interest&)> processInterest;
 };
 
-} // namespace tests
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tests
 
 /** \brief require the command in \p interest has expected prefix
  *  \note This must be used in processInterest lambda, and the Interest must be named 'interest'.