gh-444: fix exception when completing tasks

Removed code that was operating on the old subtitle version.
Replaced it with code that hopefully does something similar.  This may
not work exactly how the previous code did, but I think that's okay
because:

  - It's been the case since we started the DMR work and no one has
    complained
  - The worst that happens is that the default asignee for a task is
    wrong
Merge pull request #711 from pculture/gh-444

gh-444: fix exception when completing tasks