get Celery task status directly instead of using djcelery

Lately doing HTTP request to djcelery.views.task_status to get
Celery task status info hasn't been working. Requests have been
timing out. So just absorb the code from that view and get
directly from Celery.
rm superfluous call to collection.repo_fetch

For some reason this often uses the wrong path but also is
unnecessary because repo_behind uses cached gitstatus data.