Fixes #6949/BZ970600: remove unused tasks endpoint.

Tasks are now handled via dynflow making the tasks controller
no longer necessary.  This commit removes the controller and
the related tests and routes.

http://projects.theforeman.org/issues/6949
https://bugzilla.redhat.com/show_bug.cgi?id=970600
Merge pull request #4541 from waldenraines/6949

Fixes #6949/BZ970600: restore sorting on task status.