Disallow top-level def super and def previous_def

[makenowjust]

Because there is no way to call this.

---

Doubt. We can call such a top-level def super via a file private implicit module.

private def module_self
  self
end

def super
  p :super
end

module_self.super

But it seems like a bug because it does not compile if def module_self is public or protected.

[HertzDevil]

Can't this be done in TopLevelVisitor instead? (FunDef does a similar check there.)