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/global-configuration.cpp b/tests/global-configuration.cpp
index d3ab83a..dfae750 100644
--- a/tests/global-configuration.cpp
+++ b/tests/global-configuration.cpp
@@ -31,8 +31,7 @@
 #include <fstream>
 #include <stdlib.h>
 
-namespace nfd {
-namespace tests {
+namespace nfd::tests {
 
 class GlobalConfiguration
 {
@@ -68,5 +67,4 @@
 
 BOOST_TEST_GLOBAL_CONFIGURATION(GlobalConfiguration);
 
-} // namespace tests
-} // namespace nfd
+} // namespace nfd::tests