remove v2/support branch #3964

I'm creating this issue for findability reasons. In #3950, we have decided to remove the support/v2 branch because we are not actively applying security updates to it.

Are we keeping this branch indefinitely? If so, we should update it to use zizmor.

I don't remember a firm plan for the v2 branch. that code is accessible on main via commit history, so I don't think we really need it? I would be happy removing the branch, as opposed to doing security updates for it.

Originally posted by @d-v-b in #3950 (comment)