Edit button on legacy answers broken and unecessary

Trying to edit a legacy answer such as https://exams.vis.ethz.ch/exams/1v3d33a1.pdf#5ca8bff213be1d0012db4a36 will result in a new one being created containing the edited version instead of editing the original. This does not seem to be intended.

I think that we should just remove the edit button on legacy answers for people besides the creator.