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/mgmt/nfd/status-dataset.t.cpp b/tests/unit/mgmt/nfd/status-dataset.t.cpp
index 511498d..bb6acad 100644
--- a/tests/unit/mgmt/nfd/status-dataset.t.cpp
+++ b/tests/unit/mgmt/nfd/status-dataset.t.cpp
@@ -25,11 +25,9 @@
 #include "tests/test-common.hpp"
 #include "tests/unit/mgmt/nfd/controller-fixture.hpp"
 
-namespace ndn {
-namespace nfd {
-namespace tests {
+namespace ndn::tests {
 
-using namespace ndn::tests;
+using namespace ndn::nfd;
 
 BOOST_AUTO_TEST_SUITE(Mgmt)
 BOOST_AUTO_TEST_SUITE(Nfd)
@@ -479,6 +477,4 @@
 BOOST_AUTO_TEST_SUITE_END() // Nfd
 BOOST_AUTO_TEST_SUITE_END() // Mgmt
 
-} // namespace tests
-} // namespace nfd
-} // namespace ndn
+} // namespace ndn::tests