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/util/segment-fetcher.t.cpp b/tests/unit/util/segment-fetcher.t.cpp
index 4abe243..1166110 100644
--- a/tests/unit/util/segment-fetcher.t.cpp
+++ b/tests/unit/util/segment-fetcher.t.cpp
@@ -31,11 +31,7 @@
 
 #include <set>
 
-namespace ndn {
-namespace util {
-namespace tests {
-
-using namespace ndn::tests;
+namespace ndn::tests {
 
 class SegmentFetcherFixture : public IoKeyChainFixture
 {
@@ -853,6 +849,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestSegmentFetcher
 BOOST_AUTO_TEST_SUITE_END() // Util
 
-} // namespace tests
-} // namespace util
-} // namespace ndn
+} // namespace ndn::tests