Abandon "resource stashing" as description for catalog storage/searching

This term was a valiant experiment that never really caught on, but I think
catalog storage and searching have turned out to be not all that confusing.
Delete redundant and dodgy text in guides/exported_resources.markdown

- Stop comparing exported resources to virtual resources, no one really
  considers the similarity relevant.
- In fact, stop describing the syntax/behavior on this page entirely. That's
  what the language reference is for, so link to it.
- Collector overrides have nothing to do w/ exported resources. DELETE.