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/face.t.cpp b/tests/unit/face.t.cpp
index 9d622ed..c4ae026 100644
--- a/tests/unit/face.t.cpp
+++ b/tests/unit/face.t.cpp
@@ -31,10 +31,7 @@
 
 #include <boost/logic/tribool.hpp>
 
-namespace ndn {
-namespace tests {
-
-using ndn::util::DummyClientFace;
+namespace ndn::tests {
 
 struct WantPrefixRegReply;
 struct NoPrefixRegReply;
@@ -912,7 +909,7 @@
 {
 };
 
-typedef boost::mpl::vector<WithEnv, WithConfig> ConfigOptions;
+using ConfigOptions = boost::mpl::vector<WithEnv, WithConfig>;
 
 BOOST_FIXTURE_TEST_CASE(NoConfig, WithEnvAndConfig) // fixture configures test HOME and PIB/TPM path
 {
@@ -978,5 +975,4 @@
 
 BOOST_AUTO_TEST_SUITE_END() // TestFace
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests