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/multicast-strategy.cpp b/daemon/fw/multicast-strategy.cpp
index f49f60a..ab8e12a 100644
--- a/daemon/fw/multicast-strategy.cpp
+++ b/daemon/fw/multicast-strategy.cpp
@@ -27,8 +27,7 @@
 #include "algorithm.hpp"
 #include "common/logger.hpp"
 
-namespace nfd {
-namespace fw {
+namespace nfd::fw {
 
 NFD_REGISTER_STRATEGY(MulticastStrategy);
 
@@ -111,5 +110,4 @@
   // if nothing found, the interest will not be forwarded
 }
 
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::fw