Remove `Description` functionality.

[dantleech]

The current "description" system can be very easily generalized to act on objects instead of Puli resources.

I have created a description component and bundle, and also an enhancer for doctrine phpcr odm.

So I would suggest using this. The only difference is that the enhancers are not registered by the bundle and should be registered by the user.

(also note that all of the above is, as with this component, under development).

[dantleech]

/cc @wouterj