Comment out currently-unused class

Once the issue with slim-jwt-auth is fixed
(see tuupola/slim-jwt-auth#217),
we can reinstate that library as the JWT solution as follows:

* Add tuupola/slim-jwt-auth back into composer.json
* Remove tuupola/http-factory and tuupola/callable-handler
  (these are dependencies of tuupola/slim-jwt-auth
  and will be installed by that library; we no longer need to reference
  them directly once slim-jwt-auth is back in place)
* Uncomment body of App\Middleware\Session\JwtAuthenticationFactory class
* Remove App\Middleware\Session\JwtMiddleware file
* Remove App\Middleware\Session\JwtMiddlewareFactory file
* Uncomment lines 67-68 and remove lines 69-70 of ConfigProvider.php

For more context, see commit 3efaa3b in this repo.

service-admin/src/App/src/Middleware/Session/JwtAuthenticationFactory.php

@@ -19,7 +19,7 @@ class JwtAuthenticationFactory
      * @param ContainerInterface $container
      * @return JwtAuthentication
      */
-    public function __invoke(ContainerInterface $container)
+    /*public function __invoke(ContainerInterface $container)
     {
         $jwtConfig = $container->get('config')['jwt'];
 
@@ -45,5 +45,5 @@ public function __invoke(ContainerInterface $container)
         ];
 
         return new JwtAuthentication(array_merge($jwtConfig, $jwtHandlers));
-    }
+    }*/
 }