Word Choice – Why not ‘Hurts’ in ‘Hard Work Never Hurt Anyone’?

"One's" is a contraction of "one is" or "one has." It is also the possessive of "one." Examples of these are:

• One's mood can be affected by the seasons. (possessive)
• One's the smallest positive integer. (contraction)

"Ones" is merely the plural of "one." This is the usage you are looking for here. In English, "one" can sometimes be used to indicate individual units of something. Here are some examples. I've put in square brackets a translation of what "one" means in each instance:

• They are the ones [the specific people] who bought the house.
• I don't play video games, except ones [non-specific games] that get left at my apartment by friends.
• I am the only one [person] who can help you.
• She will take in any dogs, even ones (non-specific dogs) who are not housebroken.

Note also, there are small changes you can make to such phrases that alter the meaning very slightly. With your example, there could be many variations. I think the one you want is:

I didn't download any extra libraries except (for) the ones in the code.

The use of "for" here is optional.

It seems that your example comes from a poorly-written set of questions. 

This Mahatma Academy page includes ten questions.  The seventh matches your example. 

Of these ten, half are flawed.  Even the page as a whole is flawed, since the directions for the entire set is nonsensically repeated after the heading for the first question.  This gave me reason to wonder who is responsible for this site.  I'm still left wondering.  The about page contains WordPress example text, without a hint of the site's purpose or authorship. 

Consider the very first question offered:

Question No:1
 
Directions In the following questions, a part of the sentence is bold. Below are given alternatives to the bold part at (1), (2), (3) and (4) which may improve the sentence. Choose the correct alternative.
He told his tale of woe with tears in his eyes.

At a glance, I naturally assumed that no improvement was needed.  However, that option isn't offered:

(A) narrated
(B) recited
(C) was telling
(D) narrate

Despite the phrasing of the directions, there are no options provided at (1), (2), (3) or (4).  I can eliminate option (D) as an ungrammatical structure in model sentence.  It fails to employ proper subject/verb agreement.  The rest are grammatically sound.  Since we are given no further context, I see no reason to prefer any of them to the simple "told" of the original model. 

The provided answer key considers (A) to be correct.  I can't explain that choice.  Apparently, neither can the site, given how badly the following is formatted and phrased:

Explanation:- tell (Verb) : to give information to somebody by speaking or writing narrate (Verb) : to tell a story ; to relate Simple Past Tense ‘narrated’ will be used

This explanation, such as it is, supports leaving the verb alone at least as well as it supports the substitution.

This Mahatma Academy page certainly, and the site as a whole most likely, is too flawed to be of any use.

EverydayQuiz also references the model sentence involving Tilak, followed by the same options.  The answer key on that site sensibly lists (D) No Improvement as the correct choice.  That, at least, is an answer that I can understand and explain.