Remove the generic content component from the catalog

Apparently, the fact that the generic content component is available in the catalog is more an accident than done for a good reason.

I agreed with Mark that we remove the component from the catalog (not from the HST components library!). An extra argument for removing it is to avoid having to support questions about what exactly this component is and does. As such, the "Generic List and Content" feature turns into a "Generic List" feature only, and the plugin descriptor shall reflect this.