Prepare for new /all-jobs page

Related: gitlab-com/marketing/digital-experience/buyer-experience#3271 (closed)

gitlab-com/marketing/digital-experience/buyer-experience!3408 (merged) must be merged first.

This undoes the redirect put in place to change traffic from the broken /all-jobs page to go to our Greenhouse page. The page has been rebuilt in our Buyer Experience project. This also removes the old www page as this will no longer be needed.