Remove the implicit binder from the FnSpace in VecPerParamSpace #20526
Description
Right now there are two region binders in ty_fold: Binder<T>, and the FnSpace in VecPerParamSpace. There should be only one: Binder<T>. In fact, because of the early/late system, late-bound regions from a method or what have you cannot appear in the FnSpace predicates, but we keep this extra binding level because of the way that resolve_lifetime is structured. We should remove it.