Refactor and modernize namespace declarations

 * Completely remove inline namespace v2
 * Flatten some unnecessarily deep namespace nesting
 * Move DummyClientFace, Segmenter, SegmentFetcher to namespace ndn
 * Move all unit tests to namespace ndn::tests

Change-Id: I8bcfcf9fd669936a3277d2d5d505f765b4b05742
diff --git a/tests/unit/security/additional-description.t.cpp b/tests/unit/security/additional-description.t.cpp
index 82dd606..af71ce4 100644
--- a/tests/unit/security/additional-description.t.cpp
+++ b/tests/unit/security/additional-description.t.cpp
@@ -24,9 +24,9 @@
 
 #include "tests/boost-test.hpp"
 
-namespace ndn {
-namespace security {
-namespace tests {
+namespace ndn::tests {
+
+using ndn::security::AdditionalDescription;
 
 BOOST_CONCEPT_ASSERT((boost::EqualityComparable<AdditionalDescription>));
 BOOST_CONCEPT_ASSERT((WireEncodable<AdditionalDescription>));
@@ -99,6 +99,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestAdditionalDescription
 BOOST_AUTO_TEST_SUITE_END() // Security
 
-} // namespace tests
-} // namespace security
-} // namespace ndn
+} // namespace ndn::tests