I should be possible to create instances without constants

[bugarela]

Example, here:
https://github.com/left-curve/left-curve/blob/e0609fbadc7040effd44095926899a2a52a014da/grug/jellyfish-merkle/spec/quint/test/proofs_test.qnt#L14-L15

I just wanted two instances of the state machine to make them progress separately and compare the results. In order to achieve that, I had to come up with a constant, which was actually unnecessary. Quint wouldn't let me have instances without introducing a constant, which is silly.