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/fw/unsolicited-data-policy.cpp b/daemon/fw/unsolicited-data-policy.cpp
index b29b827..8ad0f66 100644
--- a/daemon/fw/unsolicited-data-policy.cpp
+++ b/daemon/fw/unsolicited-data-policy.cpp
@@ -28,8 +28,7 @@
 #include <boost/range/adaptor/map.hpp>
 #include <boost/range/algorithm/copy.hpp>
 
-namespace nfd {
-namespace fw {
+namespace nfd::fw {
 
 std::ostream&
 operator<<(std::ostream& os, UnsolicitedDataDecision d)
@@ -109,5 +108,4 @@
   return UnsolicitedDataDecision::CACHE;
 }
 
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::fw