Allow FS deployment scanner to treat deleting deployment content as a trigger for undeploy

Currently you have to delete the .deployed file to trigger an undeploy. FileSystemDeploymentService should also treat deleting the deployment content as a trigger.

Deleting the content is the incorrect way to trigger undeployment of an exploded archive. It's perfectly fine for a zipped deployment, but for an exploded deployment it removes the content out from under the appserver before the AS has a chance to properly undeploy.

Still, even though deleting the content as a trigger is the wrong thing to do in the exploded case, it's the more intuitive thing to do in the non-exploded case, and having the AS use it as a trigger in the exploded case doesn't increase the harm. The content is gone; the app is broken, might as well try and undeploy it.