There is a mistake in the batched delete comments part of DeleteUser which causes some comments to not be deleted
The code incorrectly updates the `start` of the limit clause resulting in most comments not being deleted.
```go
if err = e.Where("type=? AND poster_id=?", issues_model.CommentTypeComment, u.ID).Limit(batchSize, start).Find(&comments); err != nil {
```
should be:
```go
if err = e.Where("type=? AND poster_id=?", issues_model.CommentTypeComment, u.ID).Limit(batchSize, 0).Find(&comments); err != nil {
```
Co-authored-by: zeripath <art27@cantab.net>
bc4cce138a