Fix Server race conditions:

Class io_list manages children that perform asynchronous
I/O operations. The treatment of close and destruction is
refactored to fix race conditions during exit.

src/ripple/app/main/Application.cpp

@@ -520,7 +520,6 @@ public:
         m_nodeStoreScheduler.setJobQueue (*m_jobQueue);
 
         add (m_ledgerMaster->getPropertySource ());
-        add (*serverHandler_);
     }
 
     //--------------------------------------------------------------------------