Most changes are straightforward, the ones which are not straightforward:

• I removed the CART link, even with older versions where the anchor existed, the info was generic and did not add anything to what we are already saying in the doc: e.g. see this older version of the Wikipedia page
• for the pinball loss, I find the older link not that useful (see this older version of the Wikipedia page, since we are already showing the loss formula). I kept a link to the "Quantile regression" Wikipedia page.

With the changes in this PR, there are no page with broken anchor anymore.