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/daemon/table/measurements-entry.hpp b/daemon/table/measurements-entry.hpp
index a70f6e0..56825b6 100644
--- a/daemon/table/measurements-entry.hpp
+++ b/daemon/table/measurements-entry.hpp
@@ -28,13 +28,11 @@
 
 #include "strategy-info-host.hpp"
 
-namespace nfd {
-
-namespace name_tree {
+namespace nfd::name_tree {
 class Entry;
-} // namespace name_tree
+} // namespace nfd::name_tree
 
-namespace measurements {
+namespace nfd::measurements {
 
 class Measurements;
 
@@ -68,7 +66,6 @@
   friend name_tree::Entry;
 };
 
-} // namespace measurements
-} // namespace nfd
+} // namespace nfd::measurements
 
 #endif // NFD_DAEMON_TABLE_MEASUREMENTS_ENTRY_HPP