rutt: swapping order of constructors and couple of simplifications

[YaZko]

Minor simplifications to [rutt]:

• Swapped the order of constructors so that they match the definition of [eqit]
• Removed the [vclo] argument: it is introduced in [eqit] exclusively for the definition of [euttG]. If we don't define something similar here, it is completely useless
• Specialized the up-to [eqit] closure. It is only useful to prove up-to [euttge] so no need to carry all these booleans around.

Note: the up-to [eqit] closure is almost a duplicate of the one used to close [eutt] itself, except that this one is heterogeneous in [E]. We could generalize the latter and reuse it here to avoid some duplication.

Also fixed a bunch of warnings against 8.14, hope it doesn't break compatibility with older versions of Coq.

[Lysxia]

There's a missing lower bound on coq in coq-paco.dev https://github.com/coq/opam-coq-archive/pull/2002

and I've checked that it still compiles on 8.10 on my machine. I was building the wrong branch. This branch actually fails because of #[export] only being supported on hints since 8.12.

[Lysxia]

I'll just remove 8.10 and 8.11 from life support.

[liyishuai]

Need to update coq-itree.dev in opam-coq-archive accordingly.

[Lysxia]

Oh, right, I can do that!