The `Jump` instruction is useless
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Since parsley can perform generic eta-reduction on Template Haskell terms, the tail-call optimisation with Jump is actually useless.
Its original motivation was to allow call nt ret to be converted to jump nt, which would avoid constructing a new return continuation to pass down. However, the form of the return continuation in call nt ret would be x input -> retCont x input, which is ultimately eta-reduced to retCont, which is what is provided by Jump.
As such, for simplicity, it will be good to drop the Jump instruction, and ensure eta-reduction is rolled out uniformly, including to the normalisation within Lam.
Actually, not true! Loop still uses it to iterate...
But this could be Call nt Ret or even Call nt Raise, it doesn't really matter, the retCont for a loop is Void...