minor #1381 SessionServiceProvider: Remove unused property (hansott)

This PR was merged into the 2.0.x-dev branch.

Discussion
----------

SessionServiceProvider: Remove unused property

Commits
-------

3891d14f SessionServiceProvider: Remove unused property

src/Silex/Provider/SessionServiceProvider.php

@@ -29,12 +29,8 @@ use Symfony\Component\HttpFoundation\Session\Session;
  */
 class SessionServiceProvider implements ServiceProviderInterface, EventListenerProviderInterface
 {
-    private $app;
-
     public function register(Container $app)
     {
-        $this->app = $app;
-
         $app['session.test'] = false;
 
         $app['session'] = function ($app) {