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/strategy-choice.t.cpp b/tests/daemon/table/strategy-choice.t.cpp
index ff6b754..574317d 100644
--- a/tests/daemon/table/strategy-choice.t.cpp
+++ b/tests/daemon/table/strategy-choice.t.cpp
@@ -29,8 +29,7 @@
 #include "tests/daemon/global-io-fixture.hpp"
 #include "tests/daemon/fw/dummy-strategy.hpp"
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class StrategyChoiceFixture : public GlobalIoFixture
 {
@@ -335,5 +334,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestStrategyChoice
 BOOST_AUTO_TEST_SUITE_END() // Table
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests