[AS7-6552] EJB timers retaining reference to undeployed module.

On shutdown the timers indirectly retain a reference to the deployment's classloader. The attached screenshot of yourkit shows the relevant part of this link.

![timer-memory-leak](https://f.cloud.github.com/assets/1113687/171851/2ab0168e-7aa9-11e2-8290-ccc0b6d8b312.png)