table: delete deprecated functions in NameTree

NameTree::eraseEntryIfEmpty is renamed to eraseIfEmpty;
the deprecated overload that accepts shared_ptr<name_tree::Entry> is deleted.
name_tree::Entry::getPrefix is deleted in favor of getName.

This commit also improves Doxygen in NameTree class.

refs #3687

Change-Id: Ia98ca676ce6d3bc7b2e97328adccac911c8167d7

daemon/table/pit.cpp

@@ -137,7 +137,7 @@ Pit::erase(shared_ptr<pit::Entry> entry, bool canDeleteNte)
 
   nte->erasePitEntry(entry);
   if (canDeleteNte) {
-    m_nameTree.eraseEntryIfEmpty(nte);
+    m_nameTree.eraseIfEmpty(nte.get());
   }
   --m_nItems;
 }