Fix bug with remove_previously_stored_#{column} callback, when updating in a transaction, and that process is rollback

Fix bug with remove_previously_stored_#{column} callback, when updating in a transaction, and that process is rollback

The old file will be delete, but the new file name can not store success into database.

## For example:

```ruby
User.transaction do
  @user.avatar = new_file
  @user.save
  # new file stored
  # old file deleted with callback: remove_previously_stored_avatar
  # ... do bla bla
  raise ActiveRecord::Rollback
  # new file name can not update to datebase
end
```