PS: I've read through the QA section of the 2014 SO Moderator Election and seems all candidates won't allow link-only answers and will seek improvement at least (kill with fire, in most cases :)). Just want to know is there an exception and what is the current situation.
In my opinion, the answer attempts to answer the question, but needs some improvement. It was obviously answered before there were stricter standards on answering.
Before flagging it, I would first try to ask the user to improve their answer by adding the relevant excerpts from the links as they may go stale. If you're familiar with the subject, you should attempt to improve the answer yourself. Lastly, flag as low-quality.
The main reason why link-only answers are bad is because the external resource might go away, rendering the answer useless. Deleting link-only answers by itself removes just as much value and thus is harmful.
A self sufficient answer is better than a link only answer which is still better than no answer at all.
Discouraging new link-only answers is good, since it encourages posters to write self sufficient answers instead. For old answers like this one, there is no such encouragement effect, so deleting it is harmful.
Since the user who wrote this answer is still active, you should add comment encouraging him to make the answer self sufficient, instead of simply deleting it.