Revert "*Always* send a shutdown signal to enable custom shutdown actions"

This reverts commit 896899e0d6.

src/bitcoinrpc.cpp

@@ -2905,7 +2905,8 @@ void ThreadRPCServer2(void* parg)
     }
 
     vnThreadsRunning[THREAD_RPCLISTENER]--;
-    io_service.run();
+    while (!fShutdown)
+        io_service.run_one();
     vnThreadsRunning[THREAD_RPCLISTENER]++;
 }