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/net/face-uri.t.cpp b/tests/unit/net/face-uri.t.cpp
index d21d70f..34e050e 100644
--- a/tests/unit/net/face-uri.t.cpp
+++ b/tests/unit/net/face-uri.t.cpp
@@ -34,8 +34,7 @@
 
 #include <boost/concept_check.hpp>
 
-namespace ndn {
-namespace tests {
+namespace ndn::tests {
 
 BOOST_CONCEPT_ASSERT((boost::EqualityComparable<FaceUri>));
 
@@ -614,5 +613,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestFaceUri
 BOOST_AUTO_TEST_SUITE_END() // Net
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests