sched: remove the unnecessary kvs_watch_once_dir()

The sched module initialization waited for the first lwj to appear in
the kvs.  This prevented the module from completely loading until the
first lwj was submitted.  There is no need for the initialization to
wait for a lwj to appear, and so it was removed.
sched: remove completed queue

The original purpose of the completed queue was to save info on
completed jobs.  The kvs is now seen as the place to house such data
and so the scheduler can be relieved of this responsibility.
Merge pull request #9 from lipari/sched_fixes

Looks good to me all around.