Remove spec, whitepapers, request_codereview, issue_exporter from trunk.

Follows on from discussion on list, and review:
https://reviews.apache.org/r/11609/


git-svn-id: https://svn.apache.org/repos/asf/incubator/wave/trunk@1489320 13f79535-47bb-0310-9956-ffa450edef68