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/rib/readvertise/client-to-nlsr-readvertise-policy.cpp b/daemon/rib/readvertise/client-to-nlsr-readvertise-policy.cpp
index 7aff618..dcce60a 100644
--- a/daemon/rib/readvertise/client-to-nlsr-readvertise-policy.cpp
+++ b/daemon/rib/readvertise/client-to-nlsr-readvertise-policy.cpp
@@ -25,8 +25,7 @@
 
 #include "client-to-nlsr-readvertise-policy.hpp"
 
-namespace nfd {
-namespace rib {
+namespace nfd::rib {
 
 std::optional<ReadvertiseAction>
 ClientToNlsrReadvertisePolicy::handleNewRoute(const RibRouteRef& ribRoute) const
@@ -45,5 +44,4 @@
   return 1_h;
 }
 
-} // namespace rib
-} // namespace nfd
+} // namespace nfd::rib