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/tools/nfdc/rib-module.cpp b/tools/nfdc/rib-module.cpp
index 5ed8553..d0489cf 100644
--- a/tools/nfdc/rib-module.cpp
+++ b/tools/nfdc/rib-module.cpp
@@ -29,9 +29,7 @@
 #include "find-face.hpp"
 #include "format-helpers.hpp"
 
-namespace nfd {
-namespace tools {
-namespace nfdc {
+namespace nfd::tools::nfdc {
 
 void
 RibModule::registerCommands(CommandParser& parser)
@@ -410,6 +408,4 @@
   }
 }
 
-} // namespace nfdc
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tools::nfdc