Remove unnecessary readconnroute code

The check for a closed session should never be needed as the core
correctly orders the calls to the module functions. The version numbering
was also not used.

Fixed the incrementation of the query counter so that it uses relaxed
atomic operations.

server/modules/routing/readconnroute/readconnection.h

@@ -37,8 +37,6 @@
  */
 struct ROUTER_CLIENT_SES : MXS_ROUTER_SESSION
 {
-    int         rses_versno;/*< even = no active update, else odd  */
-    bool        rses_closed;/*< true when closeSession is called   */
     SERVER_REF* backend;    /*< Backend used by the client session */
     DCB*        backend_dcb;/*< DCB Connection to the backend      */
     DCB*        client_dcb; /**< Client DCB */