loolwsd: invoking disconnect on the session from Connection deadlocks

Connection thread should not attempt to disconnect the session,
which in turn will try to unload the document, which will
wait on the connection to destroy. The latter will never
happen since the connection destructor must, correctly,
wait for its thread to finish, which is waiting on itself now.

Since the session disconnect is already called from the session
destructor, there is no need to explicitly invoke it here.

Change-Id: Iaf9e8a10d4caa9001208084e909a14b4d4c5105e
Reviewed-on: https://gerrit.libreoffice.org/23966
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>
Tested-by: Ashod Nakashian <ashnakash@gmail.com>

loolwsd/LOOLKit.cpp

@@ -340,8 +340,6 @@ public:
             queue->clear();
             queue->put("eof");
             queueHandlerThread.join();
-
-            _session->disconnect();
         }
         catch (const Exception& exc)
         {