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/tests/daemon/face/lp-fragmenter.t.cpp b/tests/daemon/face/lp-fragmenter.t.cpp
index 8bd48c2..065fc6d 100644
--- a/tests/daemon/face/lp-fragmenter.t.cpp
+++ b/tests/daemon/face/lp-fragmenter.t.cpp
@@ -27,11 +27,9 @@
 
 #include "tests/test-common.hpp"
 
-namespace nfd {
-namespace face {
-namespace tests {
+namespace nfd::tests {
 
-using namespace nfd::tests;
+using namespace nfd::face;
 
 class LpFragmenterFixture
 {
@@ -174,6 +172,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestLpFragmentation
 BOOST_AUTO_TEST_SUITE_END() // Face
 
-} // namespace tests
-} // namespace face
-} // namespace nfd
+} // namespace nfd::tests