Drop risk calculation table

See https://bugs.launchpad.net/oq-engine/+bug/1374298. Notice that a companion in commonlib is required: https://github.com/gem/oq-commonlib/pull/47
The tests are running here: https://ci.openquake.org/job/zdevel_oq-engine/779
Perhaps ```hc``` might be renamed into ```calc```? (Am I understanding correctly that it could be either a hazard calculation or a risk calculation?)