fix(proof-libs) Remove fields that shouldn't be in PartialOrd.

[maximebuyse]

Fixes #1472

[W95Psp]

Those function are somehow legit: they are indeed part of that trait, but are default.

The F* backend doesn't add the default methods automatically, see #888.

But here those function will probably be missing as well if we remove them.
Can you make standalone functions named the same? e.g.

let f_lt #v_Self #v_Rhs {| t_PartialOrd v_Self v_Rhs |} (self: v_Self) (rhs: v_Rhs) = (* something with partial_cmp *)

Not sure about the naming, let's try to make something where calling f_lt works.

[W95Psp]

Thanks, that looks good to me!

[clementblaudeau]

With this change, fstar still supports the rbe examples that motivated 6dede43. Good to merge for me.