self.master.data.updates.completeBuildRequests was called twice

Each time a buildrequest is completed, in twistd.log I have: 
```
tried to complete 1 buildrequests, but only completed 0
```
This log line appears, because self.master.data.updates.completeBuildRequests is called twice.
This duplication was a symptom of bad migration from status API to direct calls to DB connector methods to the data API.  The fix is good.