Remove SyncOrder, at least temporarily (sorry fREW)

Doesn't actually work very well with the batched approach to needed
files, not documented, not exposed in UI. I'll be happy to reintegrate
if this is solved.

model/model.go

@@ -318,9 +318,6 @@ func (m *Model) NeedFilesRepo(repo string) []protocol.FileInfo {
 			fs = append(fs, f)
 			return len(fs) < indexBatchSize
 		})
-		if r := m.repoCfgs[repo].FileRanker(); r != nil {
-			files.SortBy(r).Sort(fs)
-		}
 		return fs
 	}
 	return nil