fib: implicitly delete empty Entry

Fib::removeNextHopFromAllEntries automatically deletes fib::Entry
if the last nexthop record is being removed.

refs #1341

Change-Id: I36d42fe8f9fc8f03d194f845020aff408cd70488
diff --git a/daemon/table/fib.hpp b/daemon/table/fib.hpp
index 0399833..5e2e03d 100644
--- a/daemon/table/fib.hpp
+++ b/daemon/table/fib.hpp
@@ -66,9 +66,13 @@
   size() const;
 
 private:
+  void
+  erase(const fib::Entry& entry);
+
+private:
   NameTree& m_nameTree;
   size_t m_nItems;
-  
+
   /** \brief The empty FIB entry.
    *
    *  This entry has no nexthops.